Methods and material deposition systems for forming semiconductor layers

ABSTRACT

In embodiments, an optoelectronic device comprises a substrate formed of magnesium oxide, and a multi-region stack epitaxially deposited upon the substrate. The multi-region stack may comprise a non-polar crystalline material structure along a growth direction, or may comprise a crystal polarity having an oxygen-polar crystal structure or a metal-polar crystal structure along the growth direction. In some cases, at least one region of the multi-region stack is a bulk semiconductor material comprising Mg (x) Zn (1-x) O. In some cases, at least one region of the multi-region stack is a superlattice comprising MgO and Mg (x) Zn (1-x) O.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/650,506, filed on Feb. 9, 2022, and entitled “Methods and MaterialDeposition Systems for Forming Semiconductor Layers”; which is acontinuation of U.S. patent application Ser. No. 16/949,861, filed onNov. 17, 2020, entitled “Methods and Material Deposition Systems forForming Semiconductor Layers” and issued as U.S. Pat. No. 11,282,704;which is a continuation of International Patent Application No.PCT/IB2019/054463, filed on May 29, 2019, and entitled “Methods andMaterial Deposition Systems for Forming Semiconductor Layers”; whichclaims priority to U.S. Provisional Patent Application No. 62/682,005,filed on Jun. 7, 2018, and entitled “Material Deposition System andMethods”; all of which are hereby incorporated by reference for allpurposes.

BACKGROUND

In semiconductor fabrication processes, thin film materials aredeposited on a planar deposition surface using, for example, a sourcematerial in a reaction chamber. Molecular beam epitaxy (MBE) is one ofseveral methods of depositing single crystal thin films in a reactionchamber. Molecular beam epitaxy takes place in high vacuum (HV) orultra-high vacuum (UHV) (e.g., 10⁻⁶ to 10⁻⁹ Pa). The most importantaspects of MBE are (1) the flexibility in the selection of sourcematerial species; (2) the abruptness of interfaces between dissimilarfilms deposited; (3) the low impurity levels of the films deposited; and(4) the precise and uniform thickness of the films deposited. The lastaspect is achieved by using deposition rates that are relatively slower(typically less than 1,000 nm per hour) than those of other conventionaldeposition processes like chemical vapor deposition (CVD) whichtypically exceed 10,000 nm per hour. The slow deposition rates (orgrowth rates) of MBE are used advantageously to grow the thin filmsepitaxially; however, MBE requires proportionally higher reactor vacuumto match the low impurity levels achieved by other deposition techniques(e.g. CVD).

In a deposition process like MBE, a high-quality film may have athickness uniformity of about 99% or greater across the depositionplane. Stated another way, a high-quality film may have a thicknessnon-uniformity of about 1% or less across the deposition plane.Uniformity across the deposition plane is critical in current MBEprocesses, as there is a direct correlation between the growth rate andthe quality of a film that is epitaxially grown. That is, the slowerdeposition rate enables uniform atomic monolayer-scale coverages to becontrolled across the entire deposition plane to achieve atwo-dimensional (2D) “layer-by-layer” (LbL) growth mode. Thin filmdeposition using the LbL growth mode enables a complete 2D layer to formprior to growth of subsequent layers, which is the most desirable methodfor the epitaxial growth of single crystal thin films and multilayeredheterogeneous films. Typically, the LbL growth mode is achieved for thetechnologically relevant semiconductors (e.g., AlGaAs, AlGaN, SiGe, andthe like) under at least the following criteria of: (i) highlynon-equilibrium temperature-pressure conditions; (ii) a uniform arrivalrate of species across the deposition plane; and (iii) a highly uniformspatial temperature that can be imparted to the growing surface.

SUMMARY

In some embodiments, an optoelectronic device includes a substrate and amulti-region stack epitaxially deposited upon the substrate. Themulti-region stack comprises a crystal polarity having an oxygen-polarcrystal structure or a metal-polar crystal structure along a growthdirection. The multi-region stack includes a first region comprising abuffer layer, a second region comprising a crystal structure improvementlayer, a third region comprising a first conductivity type, a fourthregion comprising an intrinsic conductivity type layer, and a fifthregion comprising a second conductivity type, where the secondconductivity type is opposite the first conductivity type. At least oneregion of the multi-region stack is a bulk semiconductor materialcomprising Mg_((x))Zn_((1-x))O. At least one region of the multi-regionstack is a superlattice comprising at least two of. ZnO, MgO andMg_((x))Zn_((1-x))O.

In some embodiments, an optoelectronic device includes a substrate and amulti-region stack epitaxially deposited upon the substrate. Themulti-region stack comprises a non-polar crystalline material structurealong a growth direction. The multi-region stack includes a first regioncomprising a buffer layer, a second region comprising a crystalstructure improvement layer, a third region comprising a firstconductivity type, a fourth region comprising an intrinsic conductivitytype layer, and a fifth region comprising a second conductivity type,where the second conductivity type is opposite the first conductivitytype. At least one region of the multi-region stack is a bulksemiconductor material comprising Mg_((x))Zn_((1-x))O. At least oneregion of the multi-region stack is a superlattice comprising at leasttwo of. ZnO, MgO and Mg_((x))Zn_((1-x))O.

In some embodiments, a method of configuring a material depositionsystem includes providing a rotation mechanism that rotates a substratearound a center axis of a substrate deposition plane of the substrate. Amaterial source that supplies a material to the substrate is selected,where the material source has i) an exit aperture with an exit apertureplane and ii) a predetermined material ejection spatial distributionfrom the exit aperture plane. The predetermined material ejectionspatial distribution has a symmetry axis which intersects the substrateat a point offset from the center axis. The exit aperture is positionedat an orthogonal distance, a lateral distance, and a tilt angle relativeto the center axis of the substrate. The method also includes settingeither i) the tilt angle or ii) the orthogonal distance and the lateraldistance for the exit aperture of the material source. A desiredaccumulation of the material on the substrate is selected to achieve adesired layer deposition uniformity for a desired growth rate. Themethod determines either i) minimum values for the orthogonal distanceand the lateral distance to achieve the desired layer depositionuniformity using the set tilt angle or ii) the tilt angle to achieve thedesired layer deposition uniformity using the set orthogonal distanceand the set lateral distance. The substrate and the material source arecontained within a vacuum environment.

In some embodiments, a method for forming semiconductor layers includesrotating a substrate around a center axis of a substrate depositionplane of the substrate, heating the substrate, and providing a materialsource that supplies a material to the substrate. The material sourcehas i) an exit aperture with an exit aperture plane and ii) apredetermined material ejection spatial distribution from the exitaperture plane, the predetermined material ejection spatial distributionhaving a symmetry axis which intersects the substrate at a point offsetfrom the center axis. The exit aperture is positioned at an orthogonaldistance, a lateral distance, and a tilt angle relative to the centeraxis of the substrate. The method also includes containing the substrateand the material source within a vacuum environment and emitting thematerial from the material source to form a semiconductor layer on thesubstrate. The exit aperture is positioned such that either i) theorthogonal distance and the lateral distance are minimized for a settilt angle, to achieve a desired layer deposition uniformity for adesired layer growth rate of the semiconductor layer on the substrate,or ii) the tilt angle is determined for a set orthogonal distance and aset lateral distance, to achieve the desired layer deposition uniformityfor the desired layer growth rate of the semiconductor layer on thesubstrate.

In some embodiments, a material deposition system has a rotationmechanism that rotates a substrate deposition plane of a substratearound a center axis of the substrate deposition plane, a heaterconfigured to heat the substrate, a material source that supplies amaterial to the substrate, and a positioning mechanism. The materialsource has i) an exit aperture with an exit aperture plane and ii) apredetermined material ejection spatial distribution from the exitaperture plane. The predetermined material ejection spatial distributionhas a symmetry axis which intersects the substrate at a point offsetfrom the center axis, where the exit aperture is positioned at anorthogonal distance, a lateral distance, and a tilt angle relative tothe center axis of the substrate. The positioning mechanism allowsdynamic adjusting of the orthogonal distance, the lateral distance, orthe tilt angle. The dynamic adjusting is based on a desired layeruniformity for a desired layer growth rate

In some embodiments, a material deposition system has a rotationmechanism that rotates a substrate around a center axis of thesubstrate. A heater is configured to heat the substrate. A positioningmechanism allows dynamic adjusting of an orthogonal distance, a lateraldistance, and a tilt angle of an exit aperture of a material sourcerelative to the substrate. The orthogonal distance, the lateraldistance, or the tilt angle depends on a predetermined material ejectionspatial distribution of the material source.

In some embodiments, a method for forming oxide-based semiconductorlayers includes rotating a substrate around a center axis of a substratedeposition plane of the substrate, heating the substrate, and placing aplurality of material sources facing the substrate. The plurality ofmaterial sources includes a magnesium (Mg) source and a plasma source ofnitrogen or oxygen. Each of the plurality of material sources has i) anexit aperture with an exit aperture plane and ii) a predeterminedmaterial ejection spatial distribution from the exit aperture plane, thematerial ejection spatial distribution having a symmetry axis whichintersects the substrate at a point offset from the center axis. Theexit aperture is positioned at an orthogonal distance, a lateraldistance, and a tilt angle relative to the center axis of the substrate.The method also includes emitting materials from the plurality ofmaterial sources onto the substrate to form an oxide-based layer on thesubstrate. The exit aperture is positioned such that either i) theorthogonal distance and the lateral distance are minimized for a settilt angle, to achieve a desired layer deposition uniformity for adesired layer growth rate of the oxide-based layer on the substrate, orii) the tilt angle is determined for a set orthogonal distance and a setlateral distance, to achieve a desired layer deposition uniformity forthe desired layer growth rate of the oxide-based layer on the substrate.

In some embodiments, a method for forming semiconductor layers includesrotating a substrate deposition plane of a substrate around a centeraxis of the substrate deposition plane, heating the substrate, andplacing a plurality of material sources facing the substrate. Theplurality of material sources includes a magnesium (Mg) source, a zinc(Zn) source, and a plasma source of nitrogen or oxygen, where each ofthe plurality of material sources has i) an exit aperture with an exitaperture plane and ii) a predetermined material ejection spatialdistribution from the exit aperture plane. The material ejection spatialdistribution has a symmetry axis which intersects the substrate at apoint offset from the center axis. The exit aperture is positioned at anorthogonal distance, a lateral distance, and a tilt angle relative tothe center axis of the substrate. Materials from the plurality ofmaterial sources are emitted onto the substrate to form a p-type dopedlayer on the substrate. The exit aperture is positioned such that eitheri) the orthogonal distance and the lateral distance are minimized for aset tilt angle, to achieve a desired layer deposition uniformity for adesired layer growth rate of the p-type doped layer on the substrate, orii) the tilt angle is determined for a set orthogonal distance and a setlateral distance, to achieve a desired layer deposition uniformity forthe desired layer growth rate of the p-type doped layer on thesubstrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a conventional high-vacuum reactionchamber.

FIG. 2 is an isometric view of a material deposition system, inaccordance with some embodiments.

FIG. 3 is a plot of examples of beam flux profiles that correspond tocertain cosine N factors of a material source, in accordance with someembodiments.

FIG. 4 through FIG. 7 are examples of plots of the configuration spacefor certain positions of the material source relative to the formationsurface, where the calculated film non-uniformity is plotted as afunction of the coordinates X and Z of the material source, inaccordance with some embodiments.

FIG. 8 is a flow diagram of an example of a method of configuring anoff-axis source in a high-vacuum reaction chamber to improve the balancebetween film quality and film growth rate, in accordance with someembodiments.

FIG. 9 is a side view of an example of a plasma treatment system used toform semiconductor layers such as high quality, oxide-based films, inaccordance with some embodiments.

FIGS. 10A-10B are cross-sectional views of oxide-based LED devicestructures, in accordance with some embodiments.

FIG. 11 is a flow diagram of an example of a method of forming the LEDdevice structures shown in FIGS. 10A-10B, in accordance with someembodiments.

DETAILED DESCRIPTION

This disclosure relates generally to semiconductor fabricationprocesses, and more particularly to material deposition systems havingan off-axis material source in a high-vacuum reaction chamber forimproving the balance between film quality and film growth rate. Methodsfor configuring the material deposition systems are disclosed, bydetermining a position of a material source and also scaling the size ofthe overall reaction chamber according to the placement of the materialsource. This disclosure also relates to high-quality, oxide-basedsemiconductor structures such as light-emitting diodes (LEDs), and thesystems and methods for forming such structures.

High film quality that can be achieved using UHV deposition techniquesis conventionally achieved by incurring a substantial increase inprocess time compared with other mature high-pressure CVD semiconductorfabrication processes. Unfortunately, best practice conventional UHVdeposition methods, such as MBE, cannot adequately accommodate the highthroughput processing demanded by silicon-based semiconductormanufacturers. Additionally, current MBE processes are limited togrowing high-uniformity films on relatively small area depositionsurfaces, such as on 6-inch diameter and smaller substrates. Thesilicon-based semiconductor industry emphasizes the importance ofscaling fabrication processes to larger deposition surfaces, such as 8-,12-, and even 18-inch deposition surfaces to maintain a sufficiently lowdeposition cost per unit area ($/m²). Therefore, new approaches areneeded for MBE processes to scale to larger deposition surfaces as wellas to provide high film quality at high deposition rates.

In semiconductor device manufacturing, group III-nitride (III-N)semiconductors (e.g., aluminum nitride, gallium nitride,aluminum-gallium nitride, indium nitride) are generally recognized asbelonging to one of the most promising semiconductor families forfabricating the wide bandgap semiconductors that are used in thefabrication of deep-ultraviolet (DUV) optical devices, such as LEDs andlaser diodes (LDs). Unfortunately, several challenges inherent toconventional manufacturing equipment and methods limit the fabricationof high-quality group III-N films.

For example, controlling the growth temperatures and precursor gaslevels necessary for high-quality film deposition is difficult withsubstrates larger than 4 inches in diameter, as mentioned above. Anon-uniform temperature profile across the film formation surface mayyield low-quality or unusable devices. Further, conventional group III-Nfilm formation is a relatively inefficient, low-throughput, andexpensive process with low utilization of costly source materials.Finally, conventional group III-N films are limited in theirdevice-bandgap tuning ability. This reduces flexibility in semiconductordevice design and application, particularly in the manufacture of DUVLEDs. As the semiconductor industry increasingly emphasizes theproduction of high-quality films on larger substrates, higher productionthroughput, and reduced manufacturing costs, new approaches for devicemanufacturing are needed.

In the present disclosure, methods of configuring an offset materialsource in a high-vacuum reaction chamber with respect to improving thebalance between film quality and film growth rate are provided. Forexample, embodiments are used to determine the position of a materialsource (e.g., a Knudsen effusion cell, a gas injector source, a remoteplasma source, an ion beam source, a sputtering source, a chargedparticle beam, a thermal evaporation source, or an ablation source) withrespect to a film formation surface in a high-vacuum reaction chamberthat provides an improved balance between film quality and film growthrate compared with the conventional art. More specifically, for a givenmaterial source that has certain attributes or characteristics, and agiven tilt angle setting for the material source, the methods are usedto determine a lateral distance and an orthogonal distance of thematerial source with respect to a formation surface for improving thebalance between film quality and film growth rate. In other embodiments,the lateral distance and orthogonal distance of the material source canbe set, and a tilt angle can be determined to achieve a desired filmquality and film growth rate.

Systems for and methods of forming a high-quality, oxide-based DUV LEDare also disclosed. Oxide-based semiconductors are wide bandgapsemiconductors classified in the II-VI semiconductor group. In general,they offer good transparency, high electron mobility, wide bandgaps, andstrong luminescence at room temperature. Oxide-based semiconductors areintrinsically n-type; conventionally, p-type doping of oxides isdifficult to accomplish. P-type doping of these semiconductors in thepresent embodiments is achieved using a plasma of active atomic nitrogen(N*) or molecular nitrogen (N₂*). The methods disclosed herein utilize aplasma reaction chamber and form films on substrates made of materialssuch as calcium fluoride. In some embodiments, a buffer layer ofmagnesium zinc oxide (MgZnO) is formed on the substrate, and anMgO—MgZnO multilayer is formed atop the buffer layer. An n-type MgZnO isthen formed atop the MgO—MgZnO multilayer, and a not-intentionally doped(NID) layer of MgZnO or MgO is formed atop the n-type MgZnO layer. Ap-type MgZnO layer is then formed using p-type doping from a plasma ofN* or N₂*. Finally, metal contacts are formed on the device structureusing a conventional lithography and metallization process. In oneexample of operation, the n-type MgZnO layer produces electrons thatmove into the NID layer, where charge carriers interact and recombine toemit light from the LED device structure in the UV wavelength range offrom about 100 nm to about 280 nm.

The methods and the materials used to form the high-quality, oxide-basedDUV LEDs exhibit advantages over conventional methods and materials. Forexample, controlling the growth temperatures and precursor gas levelsnecessary for high-quality film deposition of group III-N film withconventional methods is difficult, especially with substrates largerthan 4 inches in diameter. Further, conventional group III-N filmformation is a relatively inefficient, low-throughput, and expensiveprocess with low utilization of costly source materials. Finally,conventional group III-N films have limited bandgap-tuning ability. Thislimits flexibility in semiconductor device design and application,particularly in the production of DUV LEDs. By contrast, the methodsdisclosed herein emphasize the production of high-quality films onlarger substrates, greater device application flexibility, higherproduction throughput, and reduced manufacturing costs.

MBE is but one example of a process in which a plurality of thincrystalline films is epitaxially grown in a high-vacuum environment.Such films are composed of, for example, compound semiconductors chosenfrom the periodic table of elements. For example, IIIA-VA semiconductorsmay include group-IIIA metals chosen from at least one of Al, Ga, andIn, and group-VA species chosen from As, P, and N to createstoichiometric compositions of Al_(x)Ga_(1-x)As_(y)P_(1-y) andAl_(x)Ga_(1-x)N. In another example, II-VI semiconductors may includegroup-II metals chosen from Cd and Zn, and group-VI species chosen fromTe, S, and Se to form compound Zn_(x)Cd_(1-x)Te. Further examplesinclude IV-IV (e.g., Si_(x)Ge_(y)C_(z)) and metal oxides MO_(x). Otherexamples of metal oxides are RE-Oxides and RE-OxyNitrides (wherein RE ischosen from at least one species from the group of rare-earth elements,namely, the lanthanide series metal species or alkaline-earth metalspecies) or mixed-oxides of the form IIA-IB-VIA (e.g., Mg_(x)Zn_(1-x)O),which are also example materials fabricated using the MBE methodsdisclosed herein. The present methods can utilize other materials, suchas amorphous oxy-nitrides and metal alloys, for the creation ofhigh-uniformity films with improved growth rate. That is, the physicalprinciples disclosed herein are independent of the surface chemistryspecific to the ad-atoms and substrate.

Furthermore, the use of compound semiconductor materials in depositionprocesses provides the ability to fabricate a plurality of heterogeneousepi-layers sequentially deposited upon a deposition surface. This allowsquantum engineered structures to be tailored and optimized for specificelectro-optic and electronic applications (e.g., LEDs, lasers, powertransistors, and radio-frequency devices).

Accordingly, in the present methods and systems, a material source thatis arranged with respect to the formation surface to improve the balancebetween film quality and film growth rate is suitable for supporting acontinuous, high-throughput film formation process using an MBE system.The present disclosure provides improvements over existing systems andmethods, which are conventionally characterized by at least one of slowgrowth rates and low deposition uniformity owing to a physicalarrangement of the material source which is fixed by the manufacturer ofthe MBE system.

Conventional Material Deposition Systems

FIG. 1 is an isometric view of a portion of a high-vacuum reactionchamber 10, as known in the art, that includes a material source 18 thatis arranged off-axis and at an angle with respect to a film formationsurface 26 of a substrate 22. The high-vacuum reaction chamber 10 may bethe reaction chamber of an MBE system 5. A vacuum environment 14 ismaintained within the high-vacuum reaction chamber 10 by a vacuum pump16. For example, the vacuum environment 14 may be in the range of fromabout 10⁻¹² torr to about 10⁻⁷ torr, from about 10⁻¹¹ torr to about 10⁻⁹torr, or at about 10⁻¹¹ torr to 10⁻⁵ torr. A well-prepared andsubstantially leak-free reactor has a base pressure and growth pressure(i.e., during deposition) that is directly related to the pumping speedof the reactor and the incident beam pressures generated by the sources.

Material source 18 is arranged with respect to substrate 22 inside ofthe high-vacuum reaction chamber 10. The substrate 22 may be any basematerial on which a film or layer of material may be formed. Thesubstrate 22 is rotatable around a center axis of rotation AX. The sideof the substrate 22 that is facing the material source 18 provides thefilm formation surface 26. The substrate 22 has a radius, R_(SUB).

The formation surface 26 is the target of the material delivered fromthe material source 18. That is, the formation surface 26 is the side ofthe substrate 22 on which a film may be formed, such as by epitaxy.Epitaxy refers to the deposition of a crystalline overlayer on acrystalline substrate, where the overlayer is registered with thesubstrate. In other words, there must be one or more preferred crystalorientations of the overlayer with respect to the substrate for this tobe termed epitaxial growth. The overlayer is called an epitaxial film orepitaxial layer, and sometimes called an epi-layer.

The material source 18 may be any source of the elemental and purespecies from which a film may be formed on the formation surface 26. Forexample, the material source 18 shown in FIG. 1 may be a Knudseneffusion cell. A typical Knudsen effusion cell includes a shapedcrucible (made of high purity pyrolytic boron nitride, fused quartz,tungsten, or graphite), a plurality of resistive heating filaments, awater-cooling system, heat shields to contain the heat within thecrucible body, a crucible orifice, and an orifice shutter, none of whichare shown but are well known by those skilled in the art. The materialsource 18 includes an exit aperture 30. In the case of a Knudseneffusion cell, the exit aperture 30 is an opening in the end of thecrucible that faces the formation surface 26. As a result of crucibleheating, the material (e.g., a liquid) inside the crucible is alsoheated and material atoms are evaporated (e.g., from the liquidsurface). The number of atoms evaporated per unit area per unit of timecan be well controlled by controlling the crucible temperature. Theevaporant atoms or species are delivered under pressure from the exitaperture 30, travel with a well-defined exit velocity and with a meanfree path in excess of the source-to-substrate distance (maintained bythe high vacuum level in the reactor), and are directed toward theformation surface 26 where they collide and/or interact with thematerial of the formation surface 26. That is, a plume 34 of material(or species) that exits the exit aperture 30 of the material source 18is directed toward the formation surface 26. Plume 34 has an axis ofsymmetry SA.

Conventional, commercially-available MBE deposition systems utilizematerial sources that are spatially configured for adequate materialflux uniformity on a relatively small deposition plane area-withoutprimary regard for simultaneous optimization of both flux uniformity andgrowth rate. FIG. 1 schematically depicts the center axis of rotation AXof the substrate. The material source 18 is located a certain lateraldistance X from the center axis of rotation AX of the substrate 22, acertain orthogonal (perpendicular) distance Z from the plane of theformation surface 26, and at a virtual flux plane (VFP) tilt angle αwith respect to the plane of the formation surface 26. Hence, thematerial source 18 is an “off-axis” material source. The lateraldistance X and the orthogonal distance Z are the coordinates of thematerial source 18 with respect to the center of the substratedeposition plane 26.

In practice, non-optimal spatial placement of the material source in aconventional MBE system is compensated empirically by increasing thesubstrate-to-source distance R_(Src-Sub) (i.e., by placing the sourcesubstantially further than otherwise necessary for optimal placement).This increased substrate-to-source distance directly results in adecrease in growth rate, which is inversely proportional to the squareof the substrate-to-source distance, and a decrease in the utilizationof the expelled source material. Additionally, in conventional MBEsystems, the plume of species from the material source is typicallydirected at the center of the formation surface 26.

Conventional MBE systems can be generalized and summarized as a reactorsystem with a configuration space specified by:

-   -   (i) A symmetry axis SA of the material source plume that is        arranged to target the absolute center of rotation of the        deposition plane;    -   (ii) The source-to-substrate distance R_(src-sub) and lateral        distance X of the source VFP centroid relative to the substrate        rotation axis AX, which is configured with cylindrical or        spherical symmetry relative to the center of the deposition        plane;    -   (iii) Reactor dimensions proportioned such that X≤R_(src-sub)        and β=tan⁻¹(X/R_(src-sub))≤45°, where β is the angle between the        vertical axis Z and the symmetry axis SA; and    -   (iv) A virtual flux plane tilt angle limited in the range        0≤α≤45°.

Material Deposition System with Optimized Source Placement

FIG. 2 is an isometric view of a portion of a material deposition system50, in accordance with some embodiments. The material deposition system50—which is a molecular beam epitaxy system—has a high-vacuum reactionchamber 100. The material deposition system 50 includes a materialsource 118 that is arranged off-axis and at an angle with respect to asubstrate deposition plane 126 of a substrate 122, and is also offset byan amount R_(offset). That is, the material source 118 has a symmetryaxis SA that is aimed at a point offset from the absolute center of thesubstrate 122 by an amount R_(offset), rather than at the absolutecenter. The material source 118 deposits the material on an area 122P ofsubstrate deposition plane 126. A vacuum environment 114 is maintainedwithin the high-vacuum reaction chamber 100 by a vacuum pump 116. Forexample, the vacuum environment 114 may be in the range of from about10⁻¹² torr to about 10⁻⁷ torr in one example, from about 10⁻¹¹ torr toabout 10⁻⁹ torr in another example, or at about 10⁻¹¹ torr to 10⁻⁵ torrin yet another example.

Material source 118 is arranged with respect to substrate 122 inside ofthe high-vacuum reaction chamber 100 to produce deposition layers withhigh uniformity while maintaining a high throughput. The substrate 122may be any base material on which a film or layer of material may beformed. For example, the substrate 122 may be a wafer of silicon (e.g.,single crystal), sapphire, MgO, or Ga₂O₃ with a clean atomic surface.The substrate 122 is rotatable around a center axis of rotation AX. Thesubstrate deposition plane 126 is the side—e.g., the front surface—ofthe substrate 122 on which a film may be formed, such as by epitaxy. Thesubstrate 122 has a certain radius, R_(SUB). For example, an 8-inchsubstrate 122 has an R_(SUB) of 4 inches; a 12-inch substrate 122 has anR_(SUB) of 6 inches (approximately 150 mm); and so on. Although thesubstrate 122 shown in FIG. 1 is circular, the present systems andmethods are not limited thereto. For example, the substrate 122 may besquare or some other non-circular shape. In another embodiment, thematerial source 118 is arranged with respect to a platen or the likewhereon one or a plurality of substrates is mounted.

Those skilled in the art will recognize that the high-vacuum reactionchamber 100 may include other components (e.g., a substrate heater, amaterial source aperture, sensing devices, additional vacuum pumpingsystem components, etc.), which are not shown in FIG. 2 .

The material source 118 may be any source of the elemental and purespecies from which a film may be formed on the substrate depositionplane 126. In some embodiments, the material source may be a plasmasource of nitrogen or oxygen. Examples of the material source 118include: gaseous precursor injectors; preheated gas injectors;Knudsen-type thermally driven crucibles (i.e., Knudsen effusion cells)for containing sublimated solid material or evaporated liquid material;electron beam evaporator heating of source material; and remote plasmaactivated sources (i.e., sources wherein the plasma region is whollycontained within the source and does not extend from the source towardthe substrate surface) for gaseous feedstock. In one example, whenaluminum (Al) is the material to be epitaxially grown on the substratedeposition plane 126, the material source 118 may be a Knudsen effusioncell that contains substantially pure aluminum contained in asubstantially non-interacting crucible.

The material source 118 includes an exit aperture 130 and material level132 of the material in the material source 118. In the case of a Knudseneffusion cell, the exit aperture 130 is an opening in the end of thecrucible that faces the substrate deposition plane 126. A plume 134 ofmaterial (or species) that exits the exit aperture 130 of the materialsource 118 is directed toward the substrate deposition plane 126. Inanother embodiment, the material source 118 includes a plurality ofoutlets (exit apertures 130).

The position of material source 118 relative to the substrate 122 isdynamically adjustable such that the tilt angle, lateral distance,and/or orthogonal distance of material source 118 with respect tosubstrate 122 can be changed between production runs to achieve adesired layer deposition uniformity and desired layer growth rate. Thesettings for tilt angle, lateral distance, and orthogonal distance willdepend on the material ejection spatial distribution of the materialsource. The positioning may also be affected using multiple materialsources at the same time, that emit different materials from each other.In some embodiments, the tilt angle for the material source may be setfirst, and minimum values for the orthogonal distance and the lateraldistance can be determined using the set tilt angle. In otherembodiments, the orthogonal distance and the lateral distance may be setfirst, and the tilt angle can be determined for achieving the desiredlayer deposition uniformity for a desired growth rate. In someembodiments, the position of the material source 118 is movable whilethe substrate 122 is fixed; or the substrate 122 may be movable insteadof or in addition to the material source 118. For example, a positioningmechanism may be coupled to the material source, the substrate, or boththe material source and the substrate. The positioning mechanism may be,for example, a bracket that is secured along a slot, an arm or a postthat has an adjustable length, a linear actuator, or a combination ofthese.

The plume 134 of material (or species) is a flux of substantiallynon-interacting particles, which has a spatial beam flux profile (BFP)that can be characterized by an angular distribution of species beingemitted in a forward direction from the material source 118. The BFP canalso be referred to as a predetermined material ejection spatialdistribution of the material sources. The beam flux profile ischaracterized by the relationship of the BFP angle θ with respect to thesymmetry axis SA of the plume 134. Therefore, the material source 118may be approximated and characterized by having a certain cosine Nfactor. The cosine N factor is described in greater detail withreference to FIG. 3 .

FIG. 3 is a plot 200 of examples of beam flux profiles that correspondto certain cosine N factors of a material source. The plot 200 shows theangular beam dispersion of certain beam flux profiles as a function ofBFP angles θ. For example, the plot 200 shows a BFP 210, which has acosine N factor of 1, is substantially spherical, and is considered anisotropic point source. BFPs that have a cos^(N)(θ) with N>1 are moredirectional, as shown in FIG. 3 . For example, the plot 200 shows a BFP214, which has a cosine N factor of 6 and is a beam flux profile that iselongated and narrower than BFP 210, rather than spherical. The plot 200also shows examples of other BFPs between BFP 210 and BFP 214 that havecosine N factors between 1 and 6. By way of example, sources with acosine N factor of 1 and a cosine N factor of 6 differ in that 80% ofthe forward projected beam is contained within an angular range of±36.4° and ±15.5°, respectively. Accordingly, an improved fluxutilization can be achieved by judicious choice of cosine N factormaterial source and relative configuration position to the rotatingdeposition plane. For example, the use of sources with cosine N factorsare more directional, thus reducing the amount of material that iswasted.

The material source 118 may be any source characterized by a cosine Nfactor. This cosine N factor characterization is independent of the typeof source, whether material source 118 is a liquid source that isevaporating material, a sublimation source that is sublimating material,a gas source, or the like.

Conventional MBE systems utilize a material source that has a cosine Nfactor ranging from about 1 to about 2. It is widely believed by thoseskilled in the art that a substantially spherical plume is advantageousfor high flux uniformity. Furthermore, in conventional material sourcesthe effective cosine N factor can change as a function of sourcematerial depletion. This results in a change of spatial fluxnon-uniformity across the deposition plane as the source materialdepletes, and this problem is exacerbated if the material source isconfigured in a sub-optimal position relative to the deposition plane.Therefore, in the present embodiments it is desirable to designdeposition reactors with optimal source configurations that are tolerantof variations in effective cosine N factors.

Additionally, in conventional MBE systems, the material source is placeda relatively long distance from the formation surface and typically wellin excess of the optimal distance. Prior art systems typically employR_(src-sub) well in excess of deposition plane diameter (i.e.,R_(src-sub)>>2R_(surb) for α<45°). The typical BFP of conventionalmaterial sources characterized by cosine N factors 1<N≤2, coupled withthe long distance that the species comprising the source beam musttravel, results in at least one of a: (1) sub-optimal growth rate; (2)poor flux uniformity across the entire deposition plane; (3) a largeamount of residual background impurity species, which can deleteriouslyaffect the deposited film; and (4) poor flux utilization as measured bythe ratio of total emitted flux from the source to flux that intersectsthe deposition plane. That is, the species from the material source inconventional systems tends to be emitted throughout a substantial volumeof the chamber as opposed to being directed toward the formationsurface.

In the present methods and systems, the symmetry axis SA of the plume134 generated by the material source 118 is directed toward awell-defined portion of the periphery of the substrate deposition plane126 of the substrate 122. Specifically, the symmetry axis SA of theplume 134 is offset, being directed at a point spaced apart from thecenter of rotation of the substrate deposition plane 126. That is, thematerial source 118 has a symmetry axis SA that intersects the substrate122 at a point spaced apart from the axis of rotation AX, by an amountR_(offset).

In addition, the lateral distance X and the orthogonal distance Z thatrepresent the placement of the material source 118 from the center axisof rotation AX of the substrate deposition plane of the substrate 122,are scaled to R_(SUB). The relationship of the lateral distance X andthe vertical distance Z to R_(SUB) may be used for scaling the size ofthe high-vacuum reaction chamber 100. Enabling material sources 118 in areaction chamber 100 to be closer to the substrate 122 allows theoverall size of the reaction system (material deposition system 50) tobe smaller, thus reducing costs.

The exit aperture 130, which is the outlet of the material source 118,has an effective area A_(src), as shown in a Detail A of FIG. 2 . Theeffective area A_(src), can be defined by a radius R_(src). The exitaperture 130, which has the effective area A_(SRC), can be characterizedor designed as a plurality of independent cosine N elemental sources.For example, an integer number m of the elemental sources indexed byi={1, . . . , j, . . . , m}, wherein m>1, are each characterized by apredetermined material ejection spatial distribution (the BFP) given bycos^(Ni)(θ_(i)). The elemental sources may be chosen such that N_(i) isconstant for all values of i, or at least two dissimilar elementalsources may be chosen with Ni≠Nj.

In one example of determining placement of a material source in amaterial deposition system, a circular substrate deposition plane 126that has a radius R_(SUB)=1.5 may be used to represent a 300 mm diametersubstrate 122. A compound source (i.e., material source) of circulararea defined by a radius R_(SRC)=0.2 is positioned in the positivez-direction half space relative to the substrate deposition plane 126with center positioned at S₀(S_(0x), S_(0y), S_(0z)) and with a VFP tiltangle α=45°. The source is discretized in three radial steps ofΔρ_(SRC)=0.1 with discretized elements placed at angular intervals ofΔθ_(SRC)=36°, thereby forming a compound source plane with 21 elements.Each source of the elements is modeled as a modified cosine emitter (cosϕ_({right arrow over (n)}) _(src) _(-{right arrow over (P)}) _(DP) _(i))^(N) ^(cell) . Each source element on the VFP emits flux directedtoward the substrate deposition plane 126 parallel to the surface normal{right arrow over (n)}_(src) of VFP. The intersection of the directedflux segment with a general point P on the substrate deposition plane126 is then calculated along with the Euclidean distance norm [{rightarrow over (R)}_({right arrow over (P)}) _(DP) _(i)_(-{right arrow over (s)}) _(src) _(i) ^(i)]. The substrate 122 or thesubstrate deposition plane 126 is similarly discretized with radial andangular increments of ΔR_(SUB)=0.1 and Δθ_(SUB)=10°, thereby providing asampling mesh of 541 points with Cartesian co-ordinates P(x_(SUB),y_(SUB), z_(SUB)).

The vacuum environment of the material deposition system is sufficientfor the mean free path length for maintaining a ballistic particleregime of a material ejected from the source aperture being greater orequal to the Euclidean distance between the material source exitaperture and the point on the deposition plane that is intersected bysymmetry axis of the material ejection spatial distribution. Suitablyhigh vacuum conditions are provided in which residual backgroundimpurity species within the reaction chamber are significantly reduced.The cosine N factor of a material source also has a direct effect on theamount of residual background impurity species within a reaction chamberfor a given vacuum level. Assuming the source material is composed ofsufficiently high purity material, then the impurity concentrationsubsequently available to be incorporated into a growing film (i.e., toform an additional undesirable impurity flux component to the desirablematerial source flux) will primarily depend upon the deposition rate andthe vacuum level maintained during deposition. That is, for a given basevacuum level in the reactor prior to the introduction of the sourcematerial flux, there is a quantifiable amount of time in which awell-prepared and clean deposition surface will accumulate anundesirable impurity surface coverage. It is therefore desirable tosimultaneously achieve a small flux non-uniformity, high growth rate,and low background impurity concentration.

In the present disclosure, the material source 118, which is an offsetsource, provides both an improved flux non-uniformity across the entiresubstrate deposition plane 126 and a reduced source-to-substratedistance, as compared with conventional MBE systems. That is, optimalpositions are determined for a given material source type that achieve areduced flux non-uniformity and increased growth rate for a givensubstrate deposition plane 126 area, as compared with conventional MBEsystems.

Further, the present embodiments provide an optimal configuration spaceof material source(s) utilized in high vacuum reactors explicitly forlarge area deposition plane utility. Additionally, large deposition areareactors can be further optimized according to the methods by judiciouschoice of material source characteristics, such as effective cosine-Nfactor with N≥2 and source VFP area.

In some embodiments, the material source 118 has a cosine N factorranging from 0<N≤10, such as ranging from 2≤N≤6. Additionally, inembodiments the material source 118 is positioned optimally and close tothe substrate deposition plane 126 in comparison to prior artnon-optimal configurations. As a result, the ejected plume 134 ofdeposition species are deposited with higher efficiency onto thesubstrate deposition plane 126 than would be the case in conventionalMBE systems. A significantly shorter distance of travel of sourcematerial species provides an inverse square increase in the depositionspecies accumulation rate at the deposition surface. This leads to asignificantly lower mean free path required for the deposition speciesejected from the material source and therefore enables a substantiallycollision free regime to be maintained at a higher working pressure(i.e., at a lesser vacuum level). Yet a further advantageous property ofimproved growth rate is a reduced impact of residual background impurityspecies within the deposited film.

“Source utilization” refers to the amount (i.e., in terms of volume) ofthe material being physically ejected out of the material source 118that intersects the substrate deposition plane 126. Conventionaloff-axis MBE reactor configurations achieve at most approximately 25%source utilization. In contrast, because the present embodiments providea plume 134 which is spatially configured for an optimized target fluxnon-uniformity, the accumulation rate at the maximized and thus a higherflux utilization is realized. Furthermore, the present embodiments use ahigher directional material source (e.g., with a cosine N factor of upto about 6) than in conventional MBE (e.g., with a cosine N factor ofabout 1 to 2). Therefore, when configured optimally the presentembodiments provide yet a further increase in source utilization. Forexample, the source utilization using the present embodiments may befrom about 30% to about 50%. Therefore, the present embodiments resultin a film formation process that is more efficient than conventional MBEand achieve the optimal target flux non-uniformity with highestaccumulation rate in comparison with conventional MBE.

Furthermore, the present embodiments provide optimal high vacuumconditions for maintaining sufficiently large mean free paths of filmformation species, which enable high quality epitaxial films to beformed. The mean free path is the average distance covered by a movingparticle (e.g., an atom, a molecule, a photon) between successiveimpacts (or collisions), which modify its direction, energy, or otherproperties. More specifically, the embodiments provide high vacuumconditions for maintaining a mean free path of film formation speciesthat is greater than the distance of the material source 118 from thesubstrate deposition plane 126. For example, in order to provide a meanfree path of Al atoms of L_(MFP)>=1 meter for an example case of amaterial source beam comprised exclusively of elemental Al atomsproducing a flux of Φ_(Al)=5×10¹⁹ atoms·m⁻²·s⁻¹ directed into a reactorthat is homogeneously filled entirely of inert molecular nitrogen (N₂)at 300° K., the maximum working chamber pressure is limited to 10⁻⁶ torrand is preferably less. In practice, the longest unimpeded optical pathlength an atom is required to traverse from the source to the depositionplane should be at most L_(MFP)/2. Yet a further limitation is theeffect of the background impurity type and level specific to the type offilm to be deposited. The present embodiments can achieve high-qualityfilms if the growth rate (i.e., the time τ_(ML) for accumulating onemonolayer of desired material on the deposition plane) is desired to beat least a factor λ≥10³-10⁴ times faster than the time τ_(imp) (i.e.,τ_(imp)≥λ·τ_(ML)) required to accumulate an equivalent monolayer ofimpurity species. This places an upper limit to the acceptable residualimpurity pressure within the reactor to be of the order of 10⁻⁹-10⁻¹⁰torr.

Therefore, the mean free path of ejected species generated by thematerial source is assumed to be ballistic and collision free untilinteraction with the deposition plane. Furthermore, the base pressure ofthe reactor is assumed to be free of impurity species and notcontributing to the flux profile generated at the deposition plane.

Referring again to FIG. 2 and FIG. 3 , methods of configuring a materialdeposition system involve determining the position of a material sourcefor the purpose of improving the balance between film quality and filmgrowth rate. More than one material source can be optimized, where thesymmetry axes of each of the material sources are directed at a pointthat is offset from the axis of rotation of the substrate. For example,embodiments include determining a minimum lateral distance X and aminimum orthogonal distance Z for a given material source and tiltangle, where the material source has given parameters such as an exitaperture and material ejection spatial distribution (e.g., a givencosine N factor). In another example, embodiments include determining atilt angle for a given material source and a given lateral distance Xand orthogonal distance Z, where the material source has givenparameters such as an exit aperture and material ejection spatialdistribution (e.g., a given cosine N factor). In some embodiments, aproposed material source position (and/or angle) can be tested, and oneor more of the tilt angle α, lateral distance, orthogonal distance,desired growth rate and exit aperture geometry can be dynamicallymodified after testing to meet the desired layer uniformity. In someembodiments, if the desired layer uniformity is not met—e.g., is deemednot to be achievable—the desired layer uniformity can be changed to anew value and then new material source position parameters aredetermined to meet the new value. In some embodiments, calculation ofthe relative position between the material source and substrate can beperformed for a plurality of material sources being used together. Thatis, in some embodiments the determining of a position of a materialsource accounts for when the material source and the additional materialsources are used together. The present methods are described in greaterdetail with reference to FIG. 8 .

Optimization of Material Source Placement

FIG. 4 through FIG. 7 are examples of plots of the configuration spacefor certain positions of the material source 118 relative to thesubstrate deposition plane 126, where the calculated film non-uniformityis plotted as a function of the coordinates X and Z of the materialsource 118. The configuration spaces shown in the respective plots ofFIG. 4 through FIG. 7 are unique with respect to a certain VFP tiltangle α, a certain cosine N factor of the material source 118, and acertain R_(SUB) of the substrate deposition plane 126 (indicating thearea of film formation). The methods are not limited to only thoseconfiguration spaces shown in the plots of FIG. 4 through FIG. 7 ; theseconfiguration spaces are examples only. A configuration space exists forany combination of VFP tilt angle α, cosine N factor, and R_(SUB) valuethat is suitable for supporting a continuous, high-throughput filmformation process using MBE. Table 1 shows the configuration spaces thatcorrespond to the plots shown in FIG. 4 through FIG. 7 .

TABLE 1 Example configuration spaces VFP Tilt Angle α Cosine N FactorR_(SUB) Plot 300 of FIG. 4 45° 2 1.5 Plot 400 of FIG. 5 45° 3 1.5 Plot500 of FIG. 6 45° 6 1.5 Plot 600 of FIG. 7 30° 3 1.5

In FIG. 4 , a plot 300 shows the configuration space for positions ofthe material source 118 when the cosine N factor=2, the VFP tilt angleα=45°, and the R_(SUB)=1.5. Note that the X coordinate, the Zcoordinate, and R_(SUB) in the plot 300 are dimensionless. The plot 300shows a >15% film non-uniformity area, a 10% film non-uniformity area, a5% film non-uniformity area, a 2% film non-uniformity area, a 1% filmnon-uniformity area, a 0.5% film non-uniformity area, and a 0.3% filmnon-uniformity area, each of which is plotted as a function of thedistances X and Z of the material source 118 with respect to thesubstrate deposition plane 126. A curve 310 forms the boundary betweenthe >15% and 10% film non-uniformity areas. A curve 312 forms theboundary between the 10% and 5% film non-uniformity areas. A curve 314forms the boundary between the 5% and 2% film non-uniformity areas. Acurve 316 forms the boundary between the 2% and 1% film non-uniformityareas. A curve 318 forms the boundary between the 1% and 0.5% filmnon-uniformity areas. A curve 320 forms the boundary between the 0.5%and 0.3% film non-uniformity areas. Note that certain islands 317 of 1%film non-uniformity may exist in the 2% film non-uniformity area (i.e.,near the apex of the curve 316). Also, certain islands of 0.5% filmnon-uniformity may exist in the 1% film non-uniformity area (i.e., nearthe apex of the curve 318). Also, certain islands of 0.3% filmnon-uniformity may exist in the 0.5% film non-uniformity area (i.e.,near the apex of the curve 320).

For a given non-uniformity value, the fastest growth rate may beachieved by providing the shortest distance possible from the exitaperture 130 of the material source 118 to the substrate depositionplane 126. Therefore, the fastest growth rate may be achieved byselecting a point in the given non-uniformity area that provides theshortest possible X and Z distances (i.e., whereR_(src-sub)=(X²+Z²)^(1/2) is minimized). Short X and Z distances aredesired because the shorter the source-to-formation surface distance,the higher the growth rate, namely, the higher the throughput of the MBEsystem. By way of example and referring to the plot 300, if 2%non-uniformity is the target of the film formation process and thehighest growth rate possible is desired, a point A, which is near theapex and just inside of the curve 314, is selected to achieve theshortest possible distances X and Z, which in turn achieves the highestpossible growth rate. In this example and corresponding to the point A,the material source 118 (which has a cosine N factor=2) having a VFPtilt angle α=45° is set at a distance X of about 2.4 and a distance Z ofabout 2 to achieve about 2% non-uniformity. In another example andcorresponding to a point B, the material source 118 (which has a cosineN factor=2) having a VFP tilt angle α=45° is set at a distance X ofabout 3 and a distance Z of about 2.6 to achieve the highest possiblegrowth rate at about 1% non-uniformity.

In FIG. 5 , a plot 400 shows the configuration space for positions ofthe material source 118 when the material source 118 cosine N factor=3,the VFP tilt angle α=45°, and the R_(SUB)=1.5. Note that the Xcoordinate, the Z coordinate, and R_(SUB) in the plot 400 aredimensionless. The plot 400 shows a >15% film non-uniformity area, a 10%film non-uniformity area, a 5% film non-uniformity area, a 2% filmnon-uniformity area, a 1% film non-uniformity area, and a 0.5% filmnon-uniformity area that are plotted as a function of the coordinates Xand Z of the material source 118. A curve 410 forms the boundary betweenthe >15% and 10% film non-uniformity areas. A curve 412 forms theboundary between the 10% and 4% film non-uniformity areas. A curve 414forms the boundary between the 4% and 2% film non-uniformity areas. Acurve 416 forms the boundary between the 2% and 1% film non-uniformityareas. A curve 418 forms the boundary between the 1% and 0.5% filmnon-uniformity areas. Note that certain islands of 0.5% filmnon-uniformity may exist in the 1% film non-uniformity area (i.e., nearthe apex of the curve 418).

In one example and corresponding to a point A of the plot 400, thematerial source 118 (which has a cosine N factor=3) that has a VFP tiltangle α=45° is set at a distance X of about 3.2 and a distance Z ofabout 2.6 to achieve about 1% non-uniformity. In another example andcorresponding to a point B of the plot 400, the material source 118(which has a cosine N factor=3) that has a VFP tilt angle α=45° is setat a distance X of about 4.2 and a distance Z of about 3.5 to achieveabout 0.5% non-uniformity. Thus, for a 1% non-uniformity, the materialsource 118 should be positioned at greater X distance for a cosinefactor of 3 (point A of plot 400) than for a cosine factor of 2 (point Bof plot 300).

In FIG. 6 , a plot 500 shows the configuration space for positions ofthe material source 118 when the material source 118 cosine N factor=6,the VFP tilt angle α=45°, and the R_(SUB)=1.5. Note that the Xcoordinate, the Z coordinate, and R_(SUB) in the plot 500 aredimensionless. The plot 500 shows a >15% film non-uniformity area, a 10%film non-uniformity area, a 5% film non-uniformity area, a 2% filmnon-uniformity area, a 1% film non-uniformity area, and a 0.5% filmnon-uniformity area that are plotted as a function of the coordinates Xand Z of the material source 118. A curve 510 forms the boundary betweenthe >15% and 10% film non-uniformity areas. A curve 512 forms theboundary between the 10% and 5% film non-uniformity areas. A curve 514forms the boundary between the 5% and 2% film non-uniformity areas. Acurve 516 forms the boundary between the 2% and 1% film non-uniformityareas. A curve 518 forms the boundary between the 1% and 0.5% filmnon-uniformity areas. Note that certain islands of 5% filmnon-uniformity may exist in the 10% film non-uniformity area (i.e., nearthe apex of the curve 512). Also, certain islands of 2% filmnon-uniformity may exist in the 5% film non-uniformity area (i.e., nearthe apex of the curve 514). Also, certain islands of 1% filmnon-uniformity may exist in the 2% film non-uniformity area (i.e., nearthe apex of the curve 516). Also, certain islands of 0.5% filmnon-uniformity may exist in the 1% film non-uniformity area (i.e., nearthe apex of the curve 518).

In one example and corresponding to a point A of the plot 500, thematerial source 118 (which has a cosine N factor=6) that has a VFP tiltangle α=45° is set at a distance X of about 3.6 and a distance Z ofabout 2.6 to achieve about 1% non-uniformity. In another example andcorresponding to a point B of the plot 500, the material source 118(which has a cosine N factor=6) that has a VFP tilt angle α=45° is setat a distance X of about 3.7 and a distance Z of about 2.7 to alsoachieve about 1% non-uniformity, but at a slightly lower growth ratethan that of the point A. Thus, for a 1% non-uniformity, the materialsource 118 should be positioned at an even greater X distance for acosine factor of N=6 (point A or B of plot 500) than for a cosine factorof 3 (point A of plot 400) than for a cosine factor of 2 (point B ofplot 300).

In FIG. 7 , a plot 600 shows the configuration space for positions ofthe material source 118 when the VFP tilt angle α=30°, the materialsource 118 cosine N factor=3, and the R_(SUB)=1.5. Note that the Xcoordinate, the Z coordinate, and R_(SUB) in the plot 600 aredimensionless. The plot 600 shows a >15% film non-uniformity area, a 10%film non-uniformity area, a 5% film non-uniformity area, a 2% filmnon-uniformity area, a 1% film non-uniformity area, and a 0.5% filmnon-uniformity area that are plotted as a function of the coordinates Xand Z of the material source 118. A curve 610 forms the boundary betweenthe >15% and 10% film non-uniformity areas. A curve 612 forms theboundary between the 10% and 5% film non-uniformity areas. A curve 614forms the boundary between the 5% and 2% film non-uniformity areas. Acurve 616 forms the boundary between the 2% and 1% film non-uniformityareas. A curve 618 forms the boundary between the 1% and 0.5% filmnon-uniformity areas. Note that certain islands of 1% filmnon-uniformity may exist in the 2% film non-uniformity area (i.e., nearthe apex of the curve 616). Also, certain islands of 0.5% filmnon-uniformity may exist in the 1% film non-uniformity area (i.e., nearthe apex of the curve 618).

In one example and corresponding to a point A of the plot 600, thematerial source 118 (which has a cosine N factor=3) that has a VFP tiltangle α=30° is set at a distance X of about 3 and a distance Z of about3.3 to achieve about 1% non-uniformity. In another example andcorresponding to a point B of the plot 600, the material source 118(which has a cosine N factor=3) that has a VFP tilt angle α=30° is setat a distance X of about 3.05 and a distance Z of about 3.35 to alsoachieve about 1% non-uniformity, but at a slightly lower growth ratethan that of the point A. Comparing points A or B of plot 600 to point Aof plot 400, it is seen that for the same cosine factor N=3, changingthe tilt angle α from 30° to 45° affects the X and Z distances toachieve a 1% non-uniformity target.

FIG. 8 is a flow diagram of an example of a method 700 of configuring anoffset material source in a material deposition system to improve thebalance between film quality and film growth rate. Embodiments of themethods involve choosing values for certain variables and mathematicallymodeling the material deposition process to optimize the othervariables. For example, for a given material source type and tilt angle,the lateral distance X and orthogonal distance Z can be optimized—suchas minimizing X and Z to achieve a desired layer deposition uniformityfor a desired layer growth rate. In other example embodiments, thedistances X and Z may be fixed, and the tilt angle may be determined forachieving the desired layer deposition uniformity for the desired growthrate. In yet other embodiments, the size of the substrate (R_(SUB)) orthe type of cosine N source may be changed to meet the desireddeposition uniformity and growth rate.

Conventional MBE systems are characterized by using relatively slowgrowth rates as the means to achieve precise epi-layer thicknesses,high-uniformity flux, abrupt interfaces between heterogeneousepi-layers, high-uniformity films, high-structural films, andhigh-electronic-quality crystalline films. For example, the growth ratein conventional MBE systems may be from about 0.1 monolayers per second(ML/s) to about 10 ML/s. Furthermore, MBE systems typically require aspecialized, but straightforward, high vacuum preparation method toachieve the low residual base pressures required for low non-intentionalimpurity incorporation in the deposited films. This upfront investmentin reactor preparation toward the achievement of a vacuum state that issuitable for high quality epitaxy is a key differentiator when making acomparison with high pressure CVD reactors. Furthermore, materialsources (such as solid-liquid effusion-type sources) require front-endatmospheric preloading into the reactor, and the material sourcessubsequently become inaccessible once reactor vacuum is once againattained. Therefore, high-throughput film formation processes requirehigh flux utilization efficiency to manage epi-layer cost per unit area($/m²) for a given lifetime and total deposited film thickness of amaterial source campaign. Yet a further desired property is thescalability of reactor size to increase the total deposition area for agiven deposition cycle while maintaining low flux non-uniformity. Thisenables the cost per area (e.g., $/m²) and cost of ownership to befurther reduced. It is understood that an increased deposition surfacearea may contain a single large area substrate or a plurality of smallersubstrates advantageously positioned across the deposition plane.

In conventional MBE systems, there is a direct correlation betweengrowth rate and the distance between the material source and theformation surface (hereafter called source-to-formation surfacedistance). More specifically, the shorter the source-to-formationsurface distance, the faster the potential growth rate. The longer thesource-to-formation surface distance, the slower the growth rate.Therefore, to achieve high uniformity films, conventional MBE systemsimplement slow growth rates by placing the material source a longdistance from the formation surface in excess of the optimal position astaught herein. Consequently, to achieve high growth rates inconventional MBE systems, the source-to-formation surface distance mustbe significantly reduced, but doing so has in general compromised thefilm uniformity across the deposition plane and limited the maximumdeposition surface area (i.e., limited the scalability of the process).

By contrast, the method 700, in accordance with some embodiments,provides a technique for implementing high growth rates in an MBEprocess while still achieving high quality films. In one example, themethod 700 provides a film that has about ≥95% uniformity of thicknessacross the deposition plane (i.e., about 5% non-uniformity). In anotherexample, the method 700 provides a film that has about ≥99% uniformity(i.e., about 1% non-uniformity). The method 700 may include thefollowing steps.

At a step 710, a rotation mechanism is provided. The rotation mechanismrotates a substrate around a center axis of a substrate deposition planeof the substrate. In some embodiments, the substrate has a diameter ofequal to or greater than 6 inches (150 mm).

At a step 714, the material source is selected, including the elementalspecies of the material and the type of material source. The materialsource and the substrate are contained within a vacuum environment. Inone example of choosing a material source, if the film to be formedincludes gallium, the species selected are gallium species. In anotherexample, if the film to be formed includes aluminum, the speciesselected are aluminum species. Then, the type (i.e., gas, liquid, andsolid) of the material source 118 is selected based on the selectedspecies. In one example, if the selected species is gallium, then aKnudsen effusion cell for liquid evaporation of gallium is selected. Insome embodiments, the material source may be a cosine N source with abeam flux profile ranging, for example, from about N=1 to about N=6,which is not otherwise possible using conventional MBE. Additional(i.e., multiple) material sources may be included, where the materialsource and additional material sources are used together; that is, usedto deposit different materials onto the substrate at the same time. Insome embodiments, the material sources include a nitrogen plasma sourcethat emits active nitrogen, and an oxygen plasma material source.

Each material source 118 has an exit aperture 130 with an exit apertureplane, and a predetermined material ejection spatial distribution fromthe exit aperture plane. If more than one material source is to be used,a predetermined material ejection spatial distribution for each materialsource is acquired. In some embodiments, the exit aperture has an exitaperture geometry, and the method further comprises selecting the exitaperture geometry. The predetermined material ejection spatialdistribution has a symmetry axis which intersects the substrate at apoint offset from the center axis, where the exit aperture is to bepositioned at an orthogonal distance, a lateral distance, and a tiltangle relative to the center axis of the substrate. For a cosine Nfactor material source, the predetermined (e.g., empirically) cosine Nfactor and material ejection spatial distribution may be acquired fromthe supplier of the selected material source 118. In one example, thecosine N factor of the selected material source 118 is greater than orequal to 2, such as about 3, or up to about 6.

At a step 718, either i) the VFP tilt angle α at which to install theselected material source 118 is set or ii) the orthogonal distance andthe lateral distance for the exit aperture of the material source isset. The VFP tilt angle α of the selected material source 118 may befrom about 30° to less than 90° in one example, from about 30° to about60° in another example, or at about 45° in yet another. In one example,the selected VFP tilt angle α is 45°. The plume 134 of the materialsource 118 is provided at tilt angles that are unlike conventional MBEin which the plume 134 of the material source 118 is providedsubstantially orthogonal to the substrate deposition plane 126.

At a step 726, a desired accumulation of the material on the substrateto achieve a desired layer deposition uniformity for a desired growthrate is selected. In some embodiments, the target (desired) uniformity(or non-uniformity) value may be expressed as a flux. In someembodiments, the flux or film uniformity may be expressed as a tolerancevalue. In one example, the selected target thickness uniformity acrossthe substrate deposition plane 126 is 99% (or equivalently, 1%non-uniformity). In this disclosure, the target value may also bereferred to as a desired value. The deposition surface area (i.e., areaof the substrate deposition plane 126) is considered in thedetermination of parameters for the desired layer uniformity and desiredgrowth rate. In one example, the substrate 122 is a 3-inch wafer(R_(SUB)=1.5). In another example, the substrate 122 is a 6-inch wafer(R_(SUB)=3). In yet another example, the substrate 122 is an 8-inchwafer (R_(SUB)=4). In still another example, the substrate 122 is a12-inch (300 mm) wafer (i.e., R_(SUB)=6).

At a step 730, if the tilt angle was set in step 718, then minimumvalues for the orthogonal distance and the lateral distance to achievethe desired layer deposition uniformity are determined. That is, theshortest distances X and Z for positioning the material source 118 aredetermined using the plot of the configuration space that corresponds tothe selections made in each of the steps 714, 718 and 726. For example,the plot 400 of FIG. 5 shows the configuration space corresponding to acosine N factor=3 (selected in step 714), a VFP tilt angle α=45°(selected in step 718), and a target non-uniformity=1% (selected in step726) for an R_(SUB)=1.5. The growth rate of the film is improved bydetermining the shortest distances X and Z that correspond to theselected target uniformity. In some embodiments, the determinedorthogonal distance and the determined lateral distance of the materialsource from the substrate deposition plane is equal to or less than amean free path of the material emitted from the material source.

At step 730, if the orthogonal distance and the lateral distance wereset in step 718, then the tilt angle is determined to achieve thedesired layer deposition uniformity using the set orthogonal distanceand the set lateral distance.

In some embodiments, additional material sources may be used, and step730 involves determining either the tilt angle or the orthogonaldistance and the lateral distance for when all of the material sourcesare used together.

In some embodiments, the method of configuring the material depositionsystem is complete after step 730, for example if the determinedorthogonal and vertical distances achieve the desired layer depositionuniformity and growth rate. In an example scenario, a point is selectedwithin the 1% film non-uniformity area of the plot 400 that correspondsto the shortest, or nearly the shortest, possible distances X and Z. Inone example, the point A near the apex of the curve 416 of the plot 400is selected. The point A corresponds to a distance X of about 3.2 and adistance Z of about 2.6. Other points within the 1% film non-uniformityarea of the plot 400 may result in longer distances X and Z, therebyyielding slower growth rates. Therefore, by selecting the point A inplot 400, which is near the apex of the curve 416, the shortest, ornearly the shortest, possible distances X and Z are utilized for settingthe position of the material source 118 with respect to the substratedeposition plane 126. The growth rate is thereby improved because thecloser the material source 118 is to the substrate deposition plane 126,the higher the growth rate will be.

In further embodiments, the determined tilt angle or the determinedminimum values of the orthogonal distance and the lateral distance canbe tested to see if further optimization is needed. At a step 734, theconfiguration of the material source 118 with respect to the substratedeposition plane 126 as determined in the steps 714, 718, 726, and 730is physically implemented and tested to determine whether the targetfilm non-uniformity is achieved in combination with a suitable growthrate to support a high-throughput film formation process. For exampleand referring to FIG. 2 , the material source 118, which has a certaincosine N factor (as determined in the step 714), is positioned at thedistances X and Z from the substrate deposition plane 126 that aredetermined in the step 730 and at the VFP tilt angle α=45° that isselected in the step 718. The vacuum environment 114 of the high-vacuumreaction chamber 100 is pumped to a certain vacuum pressure (e.g., fromabout 10⁻¹¹ torr to about 10⁻⁷ torr), the rotation mechanism of step 710is used to rotate the substrate 122, and the material source 118 isactivated. Periodically, the thickness of the epitaxially grown film ismeasured at multiple sample points along the substrate deposition plane126. This measurement may be performed, for example, using a reflectionhigh-energy electron diffraction (RHEED) system that is directed at thesubstrate deposition plane 126.

At a decision step 738, based on the measurements taken in the step 734,it is determined whether both the desired non-uniformity that isselected in the step 726 and a growth rate suitably high to support ahigh-throughput film formation process have been achieved. If both thetarget non-uniformity and growth rate are achieved, the method 700 ends.Any configuration of the material source 118 with respect to thesubstrate deposition plane 126 is a balance between film quality andfilm growth rate. Therefore, if the target non-uniformity and growthrate are not achieved, either the desired film quality or the desiredfilm growth rate may be slightly relaxed. In one example, if the targetnon-uniformity is not achieved, the method 700 may proceed to a step742.

At the step 742, at least one of the tilt angle, the desired growthrate, the lateral distance, and the orthogonal distance is changed ifthe testing does not meet the desired layer deposition uniformity. Forexample, the desired growth rate may be reduced for that particularapplication (semiconductor product, manufacturing/cost goals). Themethod 700 then returns to the step 730 in which another point isselected within the desired film non-uniformity area of a certain plotof the configuration space, where the new point corresponds to aslightly greater distance X or Z, or both, and, hence, a slightlyreduced growth rate. In another example, the lateral and/or orthogonaldistances are adjusted, such as increasing their values if a slowergrowth rate is acceptable. In a further example, the tilt angle or anexit aperture geometry is changed and another iteration of method 700 isperformed, in which the material ejection spatial distributioncorresponding to the new tilt angle or exit aperture geometry is used tore-determine the orthogonal distance and the lateral distance.

In some embodiments, the desired layer deposition uniformity of the filmmay be changed at step 746 if the desired objectives are not beingattained. For example, it may be acceptable to reduce the desireduniformity of the film or increase the non-uniformity of the film for acertain application. The method 700 returns to the step 726 in which theuniformity value is reduced (i.e., the non-uniformity value isincreased), and then another iteration of the method 700 begins.

In some embodiments, the rotation mechanism and the material source arehoused in a reaction chamber, and the method 700 can also include a step750 of using a relationship of the lateral distance and the orthogonaldistance to a radius of the substrate R_(SUB) for scaling a size of thereaction chamber. For example, once minimal distances for positioningthe material sources is determined, the reaction chamber size can bescaled down. Reducing the size of the reaction chamber can providebenefits such as decreasing costs of the fabricating the chamber andoccupying less space in a manufacturing facility.

The method 700 may also include step 760 of emitting material to form asemiconductor layer. The substrate is heated while the material isemitted onto the substrate. Step 760 can include using the optimalpositioning of the material source relative to the substrate, asdetermined in step 710 through step 738. The tilt angle, the orthogonaldistance, and the lateral distance are dynamically adjustable so thatthe positioning may be adjusted according to which material source(s)are used, which may vary between runs. The tilt angle, the orthogonaldistance, and the lateral distance may be dynamically adjustable byadjusting a position of the substrate, or by adjusting the position ofthe material source.

The VFP tilt angle may be chosen in step 718 with a-priori reference tothe type of material source 118 that is chosen. For example, if thematerial source 118 is a single, open-ended orifice crucible of a liquideffusion source, then its tilt angle is limited by the inclinationrelative to the vertical direction (if placed in a gravitational field)of the crucible for a given material volume capacity and melt surfaceposition with respect to the exit aperture 130, which is the exitorifice. In general, a well-defined VFP is created at the exit planedefined by the single exit aperture 130 of a cylindrical crucible ofbody diameter D_(C) if the melt surface is sufficiently displaced fromthe exit aperture 130. Furthermore, the VFP at the exit aperture 130 maybe characterized by the aperture diameter D_(O) and aperture depthL_(O), such that D_(O)/L_(O)<1 and D_(O)<D_(C). Therefore, in practice,liquid sources are suitable when 0°<α<70°, and more preferably when30°<α<60°, and typically when 40°<α<50°. A standard configuration for alarge-capacity material source of this type is α=45°. In contrast, agas-injector material source is not constrained by the internal detailsof the source and can be used when 0°<α<90°. Clearly, a gas-injectormaterial source type is capable of grazing incidence applicationswherein 70°<α<90°.

In the operation of the high-vacuum reaction chamber 100 in which theposition of the material source 118 has been improved with respect tothe substrate deposition plane 126 according to the method 700, in oneexample, the substrate deposition plane 126 (i.e., the substrate 122) isrotating. There is a speed at which species are being ejected from thematerial source 118 and, therefore, there is an arrival rate of thespecies at the substrate deposition plane 126. The arrival rate may beexpressed, for example, in numbers of atoms or species per unit area perunit time. When the high-vacuum reaction chamber 100 is operating, therotational speed of the substrate 122 may be, for example, from about 1rpm to about 1000 rpm. However, the minimum rotational speed of thesubstrate 122 is determined by the arrival rate of the species per unittime per unit area. That is, there is a correlation between the time ittakes for one rotation at the periphery of the substrate 122 and thearrival rate of the species. The accumulation of material is averagedover one rotation of the substrate 122. For a high growth rate that issuitable to support a high throughput system, the rotational speed ofthe substrate 122 may be, for example, on the order of from about tensof rpm to about hundreds of rpm. While there is a lower limit to thefundamental deposition plane rotation speed relative to the smallestincident arrival rate of species, in general a faster rotation speed maybe advantageous.

In summary, the method 700 configures the position of the materialsource 118 with respect to the substrate deposition plane 126 toepitaxially grow a high-quality film at a growth rate suitable forsupporting a continuous, high-throughput film formation process, such asfor a continuous, high-throughput semiconductor fabrication process. Adistance of the material source 118 from the substrate deposition plane126 that is suitably short for film growth rates that are suitably highto support a high-throughput film formation process, which is nototherwise possible using conventional MBE; for example, the method mayprovide at least a 1 Angstrom per second film growth rate improvementover conventional MBE.

Oxide-Based Semiconductor Structures

The above systems, in which material sources are placed at specificallydesigned locations and angles to achieve highly uniform film layers athigh throughput growth rates, may be used to produce oxide-basedsemiconductor devices. P-type doping of various materials may also beachieved, including p-type doped Mg-based layers. For example,magnesium-based and zinc-based oxides may be formed, includingoxide-based layers of Mg_(X)Zn_(1-X)O, with x>0, p-type dopedMg_(x)Zn_(1-x)O layers where 0≤x<0.45, or a MgZnON layer. In someembodiments, the oxide-based layer is a superlattice comprisingsublayers of a) MgO and ZnO, b) MgZnO and ZnO or c) MgZnO and MgO. Insome embodiments, the oxide-based layer is a p-type doped layer, andmaterials are emitted using at least one of: active nitrogen plasma,nitrous oxide (N₂O), ammonia (NH₃), phosphorus, oxygen plasma, ordefective Mg or Zn. In this disclosure, DUV LEDs shall be described;however, other types of semiconductors may be manufactured using thesame techniques.

FIG. 9 is a side view of an example of a plasma treatment system 900that may be used to form high-quality, oxide-based films on thesubstrate 901. The plasma treatment system 900 comprises a reactionchamber 904, a heater 908, a nitrogen plasma source 912 that producesnitrogen species 916, an Mg (magnesium) source 920 that produces Mgspecies 924, a P (phosphorous) source 928 that produces P species 932,an Al (aluminum) source 936 that produces Al species 940, a Zn (zinc)source 944 that produces Zn species 948, and an oxygen plasma source 952that produces oxygen species 956. The emission of the Mg species 924 iscontrolled by a shutter 960. The emission of the Zn species 948 iscontrolled by a shutter 964. The emission of the nitrogen plasma source912, the P source 928, the Al source 936, and the oxygen plasma source952 are each similarly controlled by shutters that for the purpose ofclarity are not shown in FIG. 9 . The plasma treatment system 900 alsocomprises a vacuum pump 972, which is fluidly coupled to the reactionchamber 904. Positioning mechanisms (not shown) can be coupled to eachof the material sources 912, 920, 928, 936, 944 and 952 to adjust theposition (lateral distance, orthogonal distance, and tilt angle) of thematerial source relative to the substrate 901 to meet the desired layerdeposition specifications. A positioning mechanism (not shown) may alsobe coupled to substrate 901 to adjust and move the position of thesubstrate horizontally (in a direction of the plane of the substrate) orvertically (perpendicular to the plane of the substrate).

The plasma treatment system 900 may also include an optical detector(not shown) and/or a reflection high-energy electron diffraction (RHEED)system (not shown). The plasma treatment system 900 includes acontroller (not shown), which may be any computing device, such as ahandheld computer, a tablet computer, a laptop computer, a desktopcomputer, a centralized server, a mobile computing device, and the like.

The substrate 901 is placed in the reaction chamber 904 where it issubjected to a plasma treatment process to create defect-freeoxide-based films on the substrate 901. The substrate 901 is rotatablearound a center axis of rotation AX. The substrate 901 may be held ormanipulated using, for example, a wafer handling system (not shown). Thesubstrate 901 has a certain radius R_(SUB). For example, a 6-inchsubstrate 901 has a radius R_(SUB) of 3 inches, an 8-inch substrate 901has a radius R_(SUB) of 4 inches, a 12-inch substrate 901 has a radiusR_(SUB) of 6 inches, and so on. The side of the substrate 901 that isfacing the material sources is a film formation surface 906. The filmformation surface 906 is the surface of the substrate 901 that will besubjected to the plasma treatment process in preparation for subsequentfilm formation processes. The substrate 901 may also have a backsidecoating (not shown) for absorbing heat from the heater 908.

Whereas the material sources are located on the film formation surface906 side of the substrate 901, the heater 908 is located on the oppositeside of the substrate 901. The heater 908 is used to heat the substrate901 and, in turn, the film formation surface 906 of the substrate 901 toa growth temperature T_(g) suitable for film growth, such as a growthtemperature T_(g) of from about 300° C. to about 700° C. In one example,the heater 908 is a radiative heater with heating elements that are madeof rhenium.

The nitrogen plasma source 912 is, for example, an inductively coupledplasma (ICP) source that emits a plasma formed of N* or N₂*, shown asthe nitrogen species 916. Active nitrogen is an allotrope of nitrogenand is formed by the passage of an electrical discharge through a streamof nitrogen. Unlike the non-active nitrogen used in conventional filmformation, which has a very high bond energy that can be dissociatedonly at temperatures as high as 2,700 kelvins (K), active nitrogen maybe dissociated at relatively low temperatures (e.g., 700-800 K). Thenitrogen plasma source 912 comprises an excitation apparatus (not shown)and a pressure reducing aperture plate (not shown). Furthermore, one ormore mass flow controllers (MFC), shown as an MFC 976, is fluidlycoupled to the nitrogen plasma source 912 via a gas line 980. The MFC976 controls the gas flow rate from a gas source (not shown) containing,for example, N₂. In operation, an N₂ feedstock gas is supplied via theMFC 976 to the nitrogen plasma source 912 and is then dissociated byenergy imparted by the excitation apparatus (not shown) to produce thenitrogen species 916. The nitrogen species 916 enters thedeionizer/aperture (not shown), where substantially all the nitrogenspecies 916 that are in an excited (i.e., ionized) state are neutralizedbefore exiting the deionizer/aperture (not shown). In one example, thebeam pressure of the nitrogen species 916 is 10⁻⁸ Torr, which is a beampressure that is appropriate for doping epitaxial films.

The Mg source 920 is, for example, an effusion cell that emits the Mgspecies 924, which may be controlled using the shutter 960. In anotherexample, the Mg source 920 produces the Mg species 924 as a precursorgas. Utilizing effusion cells and precursor gases to produce the Mgspecies 924 reduces the complexity and processing costs associated withthe plasma treatment system 900. The Mg species 924 are emitted throughsublimation of solid magnesium within the Mg source 920. The flux of theMg species 924 is expressed as ((Mg). Flux is a measure of the number ofatoms per second impinging the substrate surface and is expressed as abeam pressure. In one example, ((Mg) is about 10⁻⁷ Torr.

The P source 928 is an effusion cell that emits the P species 932, whichmay be controlled using a shutter (not shown). The P species 932 may beelemental phosphorous or an allotrope of phosphorous, for example,diphosphorus (P₂) generated by sublimating gallium phosphide (GaP) orcracking tetraphosphorus (P₄) using a conventional cracker. The Pspecies 932 serves as a p-type dopant during film formation andcontributes to the formation of highly uniform oxide-based films. Theflux of the P species 932 is expressed as Φ(P). In one example, Φ(P) isabout 10⁻⁷ Torr.

The Al source 936 is, for example, an effusion cell that emits the Alspecies 940, which may be controlled using a shutter (not shown). Inanother example, the Al source 936 produces the Al species 940 as aprecursor gas. Utilizing effusion cells and precursor gases to producethe Al species 940 reduces the complexity and processing costsassociated with the plasma treatment system 900. The Al species 940 is,for example, an aluminum monospecies (e.g., pure aluminum). The flux ofthe Al species 940 is expressed as Φ(Al). In one example, Φ(Al) is about10⁻⁷ Torr. In another embodiment, instead of aluminum species, an indiummonospecies or a gallium monospecies is used.

The Zn source 944 is, for example, an effusion cell that emits the Znspecies 948, which may be controlled using the shutter 964. In anotherexample, the Zn source 944 produces the Zn species 948 as a precursorgas. Utilizing effusion cells and precursor gases to produce the Znspecies 948 reduces the complexity and processing costs associated withthe plasma treatment system 900. In the example in which the Zn source944 is an effusion cell, the Zn species 948 is formed throughsublimation of solid zinc within the Zn source 944. The flux of the Znspecies 948 is expressed as Φ(Zn). In one example, Φ(Zn) is about 10⁻⁷Torr.

The oxygen plasma source 952 is, for example, an ICP source that emits aplasma formed of one or more gases selected from the group consisting ofactive atomic oxygen (O*), molecular oxygen (O₂*), oxygen-nitrogen (ON),N*, and N₂*. The resulting plasma is shown as the oxygen species 956. Inanother example, the oxygen source 952 is a source of pure oxygensupplied to the reaction chamber 904. In the example in which the oxygenplasma source 952 is a plasma source, the oxygen plasma source 952comprises an excitation apparatus (not shown), and a deionizer/aperture(not shown). Furthermore, one or more mass flow controllers (MFC), shownas an MFC 984, an MFC 988, and an MFC 992, are fluidly coupled to theoxygen plasma source 952 via a gas line 996. The MFC 984, the MFC 988,and the MFC 992 control gas flow rates from gas sources (not shown)containing, for example, N₂, O₂, or N₂O. In one example of operation, N₂and O₂ are combined in a fixed proportion and supplied to the oxygenplasma source 952 and are then in their combined form dissociated byenergy imparted by the excitation apparatus (not shown) to produceoxygen species 956. The oxygen species 956 enters the deionizer/aperture(not shown), where substantially all the oxygen species 956 that are inan excited (i.e., ionized) state are neutralized before exiting thedeionizer/aperture (not shown). In one example, 99% of O₂ is mixed with1% of N₂ to produce a plasma of the oxygen species 956, which thenproduces a p-type doped film on the film formation surface 906. Theoxygen species 956 enhances the operating efficiency of the plasmatreatment system 900 by reducing the required processing temperaturelevels and operating costs of the plasma treatment system 900. In someembodiments, p-type doping of oxides (i.e., forming a p-type oxidelayer) is uniquely achieved by i) replacing (i.e., substituting) someoxygen atoms in the semiconductor crystal structure with nitrogen (e.g.,1 oxygen atom in every 1000), ii) replacing (i.e., substituting) some Mgor Zn atoms in the crystal structure with Al or Ga (e.g., 1 Mg or Znatom in every 10), or both (i) and (ii).

Film deposition of oxide-based films in the plasma treatment system 900occurs at from about 500° C. to about 700° C. in one example, and atabout 600° C. in another example. With the oxygen plasma source 952 inplace to enhance system efficiency, film growth in the plasma treatmentsystem 900 may occur at temperatures as low as 350° C. By contrast,conventional film deposition temperatures for group III-N materialsrange from about 900° C. to about 1,200° C., and growth temperaturetolerances must be controlled to within 5° C. The lower depositiontemperatures supported by the plasma treatment system 900 of the presentembodiments enables (1) less complex and less costly processingequipment, (2) lower process energy usage, and (3) larger growthtemperature tolerances than in conventional systems. Lower growthtemperatures and larger growth temperature tolerances facilitatehigh-quality film growth on larger substrates and, thus, higherproduction throughput.

A vacuum environment 968 is maintained within the reaction chamber 904by the vacuum pump 972. The vacuum pump 972 may be a conventionalvariable-speed vacuum pump that can evacuate the reaction chamber 904 ata certain rate known as the pumping speed. A valve (not shown) may beassociated with the vacuum pump 972. A pressure sensor (not shown) maybe provided for monitoring the vacuum pressure inside the reactionchamber 904. The vacuum pump 972 is used to maintain adequate vacuumpressure within the reaction chamber 904. The vacuum pressure within thereaction chamber 904 during film formation is, for example, from about10⁻¹¹ Torr to about 10⁻⁵ Torr.

In another embodiment of the plasma treatment system 900, pure oxygen(O₂) is supplied to the reaction chamber 904 through a heated pipe (notshown) rather than the oxygen plasma source 952. The temperature of theoxygen entering the reaction chamber 904 is, for example, from about200° C. to about 300° C. In one example, the heated pipe (not shown) isformed of sapphire.

The film formation surface 906 of the substrate 901 is the target of thematerial delivered from the nitrogen plasma source 912, the Mg source920, the P source 928, the Al source 936, the Zn source 944, and theoxygen plasma source 952. The shutter 960 is positioned in the path ofthe Mg species 924 emitted from the Mg source 920. When open, theshutter 960 allows the Mg species 924 to impinge the film formationsurface 906 of the substrate 901. When closed, the shutter 960 preventsthe Mg species 924 from impinging the film formation surface 906 of thesubstrate 901. The shutter 964 is positioned in the path of the Znspecies 948 emitted from the Zn source 944. When open, the shutter 964allows the Zn species 948 to impinge the film formation surface 906 ofthe substrate 901. When closed, the shutter 964 prevents the Zn species948 from impinging the film formation surface 906 of the substrate 901.Other shutters (not shown) similarly control the impingement of thenitrogen species 916, the P species 932, the Al species 940, and theoxygen species 956 upon the film formation surface 906 of the substrate901.

When the reaction chamber 904 is at the desired film growth temperatureT_(g) and vacuum pressure, the nitrogen plasma source 912, the Mg source920, the P source 928, the Al source 936, the Zn source 944, and theoxygen plasma source 952 are turned on. The combined impingement of thenitrogen species 916, the Mg species 924, the P species 932, the Alspecies 940, the Zn species 948, and the oxygen species 956 upon thefilm formation surface 906 of the substrate 901 forms oxide-based layerson the film formation surface 906.

FIG. 9 shows that the Mg source 920 and the Zn source 944 are located acertain lateral distance X from the center axis of rotation AX of thesubstrate 901 and a certain vertical distance Z from the plane of thefilm formation surface 906. This positioning is shown for examplepurposes. The lateral distance X and the vertical distance Z are thecoordinates of the Mg source 920 and the Zn source 944 with respect tothe center of the film formation surface 906. Further, the Mg source 920and the Zn source 944 are positioned at a virtual flux plane (VFP) tiltangle α with respect to the plane of the film formation surface 906. Thenitrogen plasma source 912, the P source 928, the Al source 936, and theoxygen plasma source 952 are each similarly positioned at a lateraldistance X from the center axis of rotation AX of the substrate 901 anda vertical distance Z from the plane of the film formation surface 906.Hence, the Mg source 920, the Zn source 944, the nitrogen plasma source912, the P source 928, the Al source 936, and the oxygen plasma source952 are “off-axis” material sources.

FIG. 10A is a cross-sectional view of an example of an LED devicestructure 1000, which is an example of an oxide-based structure to bemanufactured according to some embodiments. The LED device structure1000 is useful for forming, for example, a DUV LED. The DUV LED mayoperate in the UVC wavelength range of about 100 nm to about 280 nm. TheLED device structure 1000 may be used to form a single completed deviceor may be used to form multiple devices as part of a high-volume,high-throughput production process. The LED device structure 1000comprises a substrate 1004, upon which a plurality of oxide-based layersis deposited. Specifically, the LED device structure 1000 comprises thesubstrate 1004 on which are deposited, in order, an MgZnO buffer layer1008, an MgO—MgZnO multilayer 1012, an n-type MgZnO layer 1016, an NIDlayer 1020, and a p-type MgZnO layer 1024.

The LED device structure 1000 is an example of a lateral PIN diode. TheNID layer 1020 serves as an intrinsic heterojunction between the n-typeMgZnO layer 1016 and the p-type MgZnO layer 1024. A heterojunction isdefined as the interface between two layers of dissimilar crystallinesemiconductors that feature unequal bandgaps.

In one example, the substrate 1004 is formed of sapphire, calciumchloride, or magnesium oxide, which is substantially transparent tolight (e.g., light 1028). In this example, the thickness of thesubstrate 1004 is from about 500 μm to about 1,000 μm; further, thediameter of the substrate 1004 is from about 4 inches to about 12inches. In another example, the substrate 1004 is formed of siliconcarbide, silicon or gallium nitride (GaN), which absorbs light andtherefore is not transparent to the light 1028.

The MgZnO buffer layer 1008 is formed of MgZnO and has a thickness of,for example, from about 200 nm to about 1 μm. The MgZnO buffer layer1008 serves to minimize threading dislocations and thus reduce thedefect density in films formed atop the MgZnO buffer layer 1008.

The MgO—MgZnO multilayer 1012 is a superlattice layer formed of aplurality of alternating MgO sub-layers 1013 a and MgZnO sub-layers 1013b, where two of each sub-layer 1013 a and 1013 b are illustrated forsimplicity but may contain more sub-layers. The MgO—MgZnO multilayer1012 serves to further minimize threading dislocations and thus reducethe defect density in films formed atop the MgO—MgZnO multilayer 1012.

The n-type MgZnO layer 1016 is formed of MgZnO and is n-type doped with,for example, aluminum, gallium, or indium. Aluminum, for example, is agroup III metal with the desirable property of being highly evaporable.The n-type MgZnO layer 1016 has a thickness of, for example, from about200 nm to about 1 μm.

The NID layer 1020 is a superlattice layer of alternating sub-layers1021 a and 1021 b where two of each sub-layer 1021 a and 1021 b areillustrated for simplicity but may contain more sub-layers. Somesub-layers may be formed of, for example, intrinsic MgZnO or MgO.Additionally, the NID layer 1020 may contain one or more quantum-wellstructures formed of a narrow bandgap material. In one example, the NIDlayer 1020 is formed primarily of MgO (i.e., the barrier material) forsub-layer 1021 a, and contains one or more narrow bandgap ZnOquantum-well sub-layers 1021 b. The NID layer 1020 has a thickness of,for example, from about 10 nm to about 50 nm. In another example, theNID layer 1020 is formed as a superlattice structure using a MgZnO orMgZnO—ZnO alloy.

The p-type MgZnO layer 1024 is formed of, for example, nitrogen-dopedMgZnO and has a minimum thickness of, for example, about 200 nm. P-typedoping of the p-type MgZnO layer 1024 is achieved using, for example, aplasma of N* or N₂* according to the method described below in referenceto FIG. 11 . In another example, p-type doping of the p-type MgZnO layer1024 is achieved using independent sources of nitrous oxide (N₂O) orammonia (NH₃). The p-type MgZnO layer 1024 provides the ability to tunethe bandgap of the device across a broad wavelength range, whereasconventional group III-N films are limited in their bandgap-tuningability. For example, it is extremely difficult to create a UV LEDoperating at 190 nm (i.e., 6 eV) or below using AlN alone. In somecases, boron-AlN compounds may be used. However, this material entailshigh levels of nitrogen and high deposition temperatures, both of whichmay be extremely costly, technically infeasible, and/or commerciallyinfeasible. Moreover, it is quite problematic to dope boron-AlNcompounds to an electrical conductivity type. In contrast, p-type MgZnOfilms can be produced at easily achieved deposition temperatures and canbe doped to p-type conductivity with easily achieved levels of nitrogen.

Following the formation of the p-type MgZnO layer 1024, electricalcontacts (e.g., anodes and cathodes; not shown) are formed usingstandard metallization and lithographic processing. The electricalcontacts are formed of, for example, nickel (Ni), palladium (Pd),titanium (Ti), aluminum (Al), titanium nitride (TiN), or titaniumaluminum (TiAl).

In one example, the epitaxial layers of the LED device structure 1000are deposited such that the charge carriers (i.e., electrons and holes)move vertically and light (i.e., photons), shown as light 1028 in FIG.10A, is also emitted vertically. In another example, the epitaxiallayers of the LED device structure 1000 are deposited such that thecharge carriers move laterally, and light is also emitted laterally.“Laterally” in FIG. 10A refers to the direction substantially along theplane of the layer growth, while “vertically” refers to the directionsubstantially perpendicular or normal to the plane of the layer growth.

In operation, the n-type MgZnO layer 1016 produces electrons that movevertically into the NID layer 1020. Continuing the example, the p-typeMgZnO layer 1024 emits holes that move vertically into the NID layer1020. The charge carriers interact and recombine within the NID layer1020 and are emitted as light 1028 from the LED device structure 1000.In the example in which the LED device structure 1000 is a UVC LED, theNID layer 1020 is designed to emit light in the wavelength range of fromabout 100 nm to about 280 nm. In the example in which the substrate 1004is substantially transparent to light, a certain percentage of the lightemitted from the NID layer 1020 is emitted directly through thesubstrate 1004.

FIG. 10B is a cross-sectional view of an optoelectronic device embodiedas an LED device structure 1030, in which a multi-region stack 1031comprises a crystal polarity that has either an oxygen-polar crystalstructure or metal polar crystal structure along a growth direction1032. The growth direction 1032 is vertical in FIG. 10B, relative to thehorizontal plane of the layers of the multi-region stack 1031. The LEDdevice structure 1030 is useful for forming, for example, a DUV LED. TheDUV LED may operate in the UVC wavelength range of about 100 nm to about280 nm. The LED device structure 1030 may be used to form a singlecompleted device or may be used to form multiple devices as part of ahigh-volume, high-throughput production process. The LED devicestructure 1030 has a substrate 1034, upon which the crystal polarmulti-region stack 1031 of at least five regions is epitaxiallydeposited. The multi-region stack 1031 includes regions (i.e., layers)1038, 1042, 1046, 1050 and 1054.

In one embodiment, the substrate 1034 is formed of sapphire, calciumchloride, or magnesium oxide, which is substantially transparent tolight (e.g., light 1058). In this example, the thickness of thesubstrate 1034 may be from about 500 μm to about 1,000 μm. The diameterof the substrate 1034 may be from about 4 inches to about 12 inches. Inanother example, the substrate 1034 is formed of silicon carbide,silicon or gallium nitride (GaN), which absorbs light and therefore isnot transparent to the light 1058.

A first region 1038 of the multi-region stack 1031 is a buffer layerthat is formed on a surface of the substrate 1034. First region 1038serves to improve the atomic surface quality of the substrate 1034 byminimizing threading dislocations and thus reducing the defect densityin films formed atop the first region 1038. A second region 1042 onbuffer layer 1038 serves as a crystal structure improvement layer. Thesecond region 1042 further minimizes threading dislocations and thusreduces the defect density in films formed atop the second region 1042.

A third region 1046 on second region 1042 has a first conductivity type,such as n-type or p-type conductivity. A fifth region 1054 has a secondconductivity type, with a fourth region 1050 being an intrinsicconductivity type (NID) layer in between third region 1046 and fifthregion 1054. The second conductivity type is opposite the firstconductivity type. For example, if third region 1046 is n-type, thenfifth region 1054 is p-type. Conversely, if third region 1046 is p-type,then fifth region 1054 is n-type.

The multi-region stack 1031 includes at least one region (i.e., layer)that is a bulk semiconductor material comprising Mg_((x))Zn_((1-x))O andat least one region that is a superlattice, where the superlatticecomprises at least two compositions selected from ZnO, MgO andMg_((x))Zn_((1-x))O. In one embodiment, the buffer layer (first region1038) may be made of MgZnO with a thickness of, for example, from about200 nm to about 1 μm. In one embodiment, the second region 1042 is asuperlattice layer formed of a plurality of alternating MgO sub-layers1043 a and MgZnO sub-layers 1043 b, where two of each sub-layer 1043 aand 1043 b are illustrated for clarity but may contain more sub-layers.

In some embodiments, at least one of the third region 1046 or the fifthregion 1054 (the n-type or p-type conductivity layers) is formed byintroducing at least one of silicon, germanium, nitrogen, aluminum,gallium, nickel, or phosphorous into the oxygen-polar or a metal-polarcrystal structure of the multi-region stack 1031. In some embodiments,at least one of the third region 1046 or the fifth region 1054 is formedusing compositional grading of a bulk or bulk-like composition of theform of Mg_((x))Zn_((1-x))O. X is a spatially dependent value thatvaries along the growth direction. That is, the third region 1046 or thefifth region 1054 may be comprised of a spatially dependent compositionof Mg_((x))Zn_((1-x))O that changes along the oxygen-polar ormetal-polar (vertical in FIG. 10B) growth direction 1032. An example ofcompositional grading is represented by the gradient shading in thirdregion 1046 in FIG. 10B.

In some embodiments, at least one of the third region 1046 or the fifthregion 1054 (the n-type or p-type conductivity layers) is formed usingcompositional grading of an effective alloy composition of asuperlattice. The superlattice has a plurality of bilayer pairs formedof alternating layers of Mg_((x))Zn_((1-x))O and Mg_((y))Zn_((1-y))O,where x≠y. The effective alloy composition of the superlattice variesspatially along the growth direction. That is, the spatially dependenteffective alloy of the superlattice, as determined by x and y, variesalong the oxygen-polar or metal-polar growth direction 1032. An exampleof a compositional grading of a superlattice is represented by fifthregion 1054 in FIG. 10B, in which sub-layers 1055 a 1 and 1055 a 2 maybe Mg_((x))Zn_((1-x))O and sub-layers 1055 b 1 and 1055 b 2 may beMg_((y))Zn_((1-y))O. The alternating sub-layers of Mg_((x))Zn_((1-x))Oand Mg_((y))Zn_((1-y))O form bilayers. For sub-layers 1055 a 1 and 1055a 2, x changes along the growth direction 1032. Similarly, forsub-layers 1055 b 1 and 1055 b 2, y changes along the growth direction1032.

In other embodiments, FIG. 10B may also represent optoelectronicdevices, such as LEDs, having non-polar crystalline material structures.In such embodiments, the multi-region stack 1031 comprises a non-polarcrystalline material structure along the growth direction 1032. Similarto the polar crystal structure described above, the multi-region stack1031 for a non-polar crystalline structure includes regions (i.e.,layers) 1038, 1042, 1046, 1050 and 1054. First region 1038 of themulti-region stack 1031 is a buffer layer that is formed on a surface ofthe substrate 1034. Second region 1042 on buffer layer 1038 serves as acrystal structure improvement layer. Third region 1046 on second region1042 has a first conductivity type, such as n-type or p-typeconductivity. Fourth region 1050 is an intrinsic conductivity type (NID)layer. Fifth region 1054 has a second conductivity type opposite thefirst conductivity type. At least one region of the multi-region stack1031 is a bulk or bulk-like semiconductor material comprisingMg_((x))Zn_((1-x))O. At least one region of the multi-region stack 1031is a superlattice, where the superlattice comprises at least twocompositions selected from ZnO, MgO and Mg_((x))Zn_((1-x))O.

In some embodiments of a non-polar crystalline structure of FIG. 10B, atleast one of the third region 1046 or the fifth region 1054 is formed byintroducing at least one of silicon, germanium, nitrogen, aluminum,gallium, nickel or phosphorous into the non-polar crystalline materialstructure. In some embodiments, at least one of the third region 1046 orthe fifth region 1054 (n-type or p-type conductivity regions) is formedusing compositional grading of an elective alloy composition of asuperlattice, where the superlattice has a plurality of bilayer pairsformed of Mg_((x))M_((1-x))O/Mg_((y))M_((1-y))O, in which x y and M isselected from Zn, Al, Ga, Ni, N, and P. The effective alloy compositionof the superlattice varies along the growth direction (i.e., x and y arespatially dependent in the growth direction). For example, for fifthregion 1054, sub-layers 1055 a 1 and 1055 a 2 may be Mg_((x))M_((1-x))Owhile sub-layers 1055 b 1 and 1055 b 2 may be Mg_((y))M_((1-y))O. Insome embodiments, the multi-region stack 1031 consists of (i.e., all thecompositions of the multi-region stack 1031 are selected from)Mg_((x))M_((1-x))O compositions, where 0.55<x≤1.0, and M is selectedfrom Zn, Al, Ga, Ni, N, and P.

FIG. 11 is a flow diagram of an example of a method 1100 for forminghigh-quality, oxide-based LED device structures using, for example, theplasma treatment system 900 of FIG. 9 . The method 1100 comprises thesteps below which shall be described using the device structure 1000 ofFIG. 10A but may also apply to the device structures of FIG. 10B andother oxide devices.

Step 1110 involves rotating a substrate around a center axis of asubstrate deposition plane of the substrate and heating the substrate.The substrate is loaded in a reaction chamber in preparation forproducing a high-quality, oxide-based LED. The substrate is formed of,for example, calcium fluoride, MgO (111) and (001) surface orientations,Ga₂O₃ (−201) and (010) surface orientations, Al₂O₃ (c-plane andr-plane), Si (111), Si (001), rare-earth oxide buffer layers, or MgZnOsuperlattice buffer layers. Using a vacuum pump, the vacuum pressureinside the reaction chamber is pumped down to about 10⁻⁵ Torr or less toevacuate the chamber such that the substrate is contained within avacuum environment. Further, a heater is activated to provide a desiredgrowth temperature T_(g) at a film formation surface of the substrate.

Step 1115 includes providing at least one material source that suppliesa material to the substrate. The material source is contained within thevacuum environment of the reaction chamber. Each material source has i)an exit aperture with an exit aperture plane and ii) a predeterminedmaterial ejection spatial distribution from the exit aperture plane. Thepredetermined material ejection spatial distribution has a symmetry axiswhich intersects the substrate at a point offset from the center axis.The exit aperture is positioned at an orthogonal distance, a lateraldistance, and a tilt angle relative to the center axis of the substrate.All material sources in the plasma reaction chamber are activated whilethe shutters remain closed. The material sources may include, forexample, one or more of a nitrogen plasma source, a Mg source, a Psource, an Al source, a Zn source, a nitrous oxide (N₂O) source, anammonia (NH₃) source and an oxygen plasma source which are activatedwhile their associated shutters remain closed so that no species impingethe film formation surface of the substrate.

Step 1120 involves emitting material from the material sources to formsemiconductor layers on the substrate, such as oxide-based layers andp-type doped layers. Step 1120 may include steps 1122, 1125, 1130, 1135,1140 and 1145 for forming individual layers of the semiconductor device.During the emitting of step 1120, the exit aperture for at least one ofthe material sources is positioned such that either i) the orthogonaldistance and the lateral distance are minimized for a set tilt angle, toachieve a desired layer deposition uniformity for a desired layer growthrate of the semiconductor layer on the substrate, or ii) the tilt angleis determined for a set orthogonal distance and a set lateral distance,to achieve the desired layer deposition uniformity for the desired layergrowth rate of the semiconductor layer on the substrate.

The layers of device structure 1000 of FIG. 10A shall now be used todescribe the steps of FIG. 11 ; however, other layers may be formedusing the methods and systems disclosed herein. At step 1122, the MgZnObuffer layer (e.g., layer 1008) is formed to a desired thickness.Namely, the shutters associated with the oxygen plasma source, Mgspecies (e.g., shutter 960) and Zn species (e.g., shutter 964) areopened, and thereby the oxygen species impinges the film formationsurface of the substrate. In one example, the thickness of the MgZnObuffer layer formed is about 200 nm. During film growth, the vacuumpressure inside the reaction chamber is maintained via the vacuum pumpat about 10⁻⁵ Torr or less to ensure ballistic transport of the Mgspecies, the Zn species, and the oxygen species to the film formationsurface of the substrate.

At step 1125, the MgO—MgZnO multilayer (e.g., layer 1012) is formed to adesired thickness. Namely, the shutters associated with the oxygenplasma source, Mg species and Zn species are opened, and thereby theoxygen species impinges the film formation surface of the substrate toform the MgZnO component (sub-layer) of the MgO—MgZnO multilayer. Theshutter for the Zn species (e.g., shutter 964) is then closed to formthe MgO component (sub-layer) of the MgO—MgZnO multilayer. The Znshutter is alternately opened and closed during formation of themultiple respective sub-layers of the superlattice MgO—MgZnO multilayeruntil a desired layer thickness is achieved.

At step 1130, the n-type MgZnO layer (e.g., layer 1016) is formed to adesired thickness. Namely, the shutters associated with the oxygenplasma source, Mg species and Zn species are opened, and thereby theoxygen species impinges the film formation surface of the substrate toform the MgZnO component of the n-type MgZnO layer. Simultaneously, theshutter that controls the Al source is opened and the Al speciesimpinges the film formation surface of the substrate to serve as ann-type dopant in the n-type MgZnO layer.

At step 1135, the NID layer (e.g., layer 1020) is formed to a desiredthickness. In the example in which the NID layer contains one or morequantum-well structures formed of narrow bandgap zinc-oxide (ZnO)quantum-well sub-layers, the MgO barrier material is formed by openingthe Mg shutter (e.g., shutter 260) and the shutter associated with theoxygen plasma source to allow the Mg species and the oxygen species toimpinge the film formation surface of the substrate. The ZnOquantum-well sub-layers are formed by simultaneously closing the Mgshutter and opening the Zn shutter (e.g., shutter 264) to allow the Znspecies to impinge the film formation surface of the substrate. The Mgand Zn shutters are alternately opened and closed during the formationof the multiple respective sub-layers of the NID layer until a desiredlayer thickness is achieved. In one example, the thickness of the NIDlayer is about 25 nm.

At step 1140, the p-type MgZnO layer (e.g., layer 1024) is formed to adesired thickness. Namely, the shutters associated with the oxygenplasma source, Mg species and Zn species are opened, and thereby theoxygen species impinges the film formation surface of the substrate toform the MgZnO component of the p-type MgZnO layer. Simultaneously, theshutter associated with the nitrogen plasma source is opened and therebythe nitrogen species impinge the film formation surface of thesubstrate. The nitrogen species are, for example, N* or N₂* and serve asa p-type dopant in the p-type MgZnO layer. A beam flux monitor, such asa RHEED system, may be used to monitor the flux of the nitrogen species.

At step 1145, electrical contacts are formed on the LED device structure(e.g., device 1000) using a conventional lithographic and metallizationprocess. The LED device structure is a vertical conduction LED in whichcharge carriers interact and recombine within the NID layer to generatethe light emitted from the LED device structure. In another example, themethod 1100 is used to form a lateral conduction LED in which lightemission occurs laterally.

In summary, the plasma treatment systems and the methods of forminghigh-quality, oxide-based devices (e.g. DUV LEDs) exhibit advantagesover conventional systems for and methods of forming group III-N filmsusing epitaxial growth. Conventional semiconductor manufacturingequipment and epitaxial processes are unable to maintain the film growthtemperature tolerances and precursor gas levels necessary forhigh-quality film deposition, especially for substrates larger than 4inches in diameter. This limitation may result in non-uniformtemperature profiles across the film formation surface and thereforeyield low-quality or unusable devices. Finally, conventional group III-Nfilms are limited in their device bandgap tuning ability. This limitsflexibility in semiconductor device design and application, particularlyin the manufacturing of DUV LEDs. In contrast, the present plasmatreatment systems and methods disclosed herein emphasize the productionof high-quality films on larger substrates, greater device applicationflexibility, higher production throughput, and reduced manufacturingcosts.

The present methods and systems may be used in general to formstructures having one or more MgZnO layers, thus providing metal-richand/or oxygen-rich compositions. These are classed as non-stoichiometricmaterials and exhibit oxygen and/or metal vacancies which can beengineered to exhibit excess electrons or holes depending on thecrystallographic defect introduced in the crystal. In some embodiments,the structures are Mg_(y)Zn_(1-y)O/Mg_(x)Zn_(1-x)O superlattices orMgZn(O,N) oxynitride compositions. For example, the semiconductor layersmay be a superlattice comprising sublayers of a) MgO and ZnO, b) MgZnOand ZnO or c) MgZnO and MgO.

Examples of MgZnO structures that are grown according to the presentembodiments include MgO as a layer and substrate; an Mg_(x)Zn_(1-x)Olayer, with x>0.5 (rocksalt); and MgO/Mg_(x)Zn_(1-x)O, x>0.55 (non-polarrocksalt). In some embodiments, polar structures comprising wurtziticMg_(x)Zn_(1-x)O, x<0.45 may be fabricated, such as superlattices ofMg_(x)Zn_(1-x)O, where 0≤x<0.45; superlattices of [Mg_(x)Zn_(1-x)O,0≤x<0.45]/[Mg_(y)Zn_(1-y)O, 0≤y<0.45], where x≠y; and gradedcompositions of bulk Mg_(x)Zn_(1-x)O, 0≤x<0.45. The graded compositionsof bulk Mg_(x)Zn_(1-x)O can include p- or n-type doping that is induced.For example, some methods can induce p-type by grading WBG to NBG forO-polar on substantially C-plane oriented, or by grading NBG to WBG formetal-polar on substantially C-plane oriented. In other examples,methods can induce n-type by grading WBG to NBG for metal-polar onsubstantially C-plane oriented, or by grading NBG to WBG for O-polar onsubstantially C-plane oriented. In some embodiments, a graded effectivealloy composition can be created by grading a superlattice unit cellusing the bulk criteria described for bulk Mg_(x)Zn_(1-x)O.

In addition to the polarization-type doping as described in the previousparagraph, impurity type doping may also be used. In some embodiments,both impurity and polarization type doping can be used.

Other embodiments include forming a device using polarization doping ofMgZnO for compositions x<0.45. Yet other embodiments include forming amixed type superlattice comprising MgO/ZnO, or comprising a superlatticeof [Mg_(x)Zn_(1-x)O, 0≤x≤1]/[Mg_(y)Zn_(1-y)O, 0≤y≤1], where x≠y. Yetfurther embodiments include forming non-polar Mg_(x)Zn_(1-x)Ostructures, where x>0.55.

The structures may be grown on various substrates, such as: MgO (111)and (001) surface orientations, Ga₂O₃ (−201) and (010) surfaceorientations, Al₂O₃ (c-plane and r-plane), Si (111) for use withwurtzitic MgZnO x<0.45, Si (001) for use with MgZnO x>0.55, rare-earthoxide buffer layers, and MgZnO superlattice buffer layers.

MgZnO superlattices and multiple quantum wells (MQWs) enable thickerlayers for quantization effects, and are easier to grow than AlGaN orAlN/GaN superlattices.

Reference has been made in detail to embodiments of the disclosedinvention, one or more examples of which have been illustrated in theaccompanying figures. Each example has been provided by way ofexplanation of the present technology, not as a limitation of thepresent technology. In fact, while the specification has been describedin detail with respect to specific embodiments of the invention, it willbe appreciated that those skilled in the art, upon attaining anunderstanding of the foregoing, may readily conceive of alterations to,variations of, and equivalents to these embodiments. For instance,features illustrated or described as part of one embodiment may be usedwith another embodiment to yield a still further embodiment. Thus, it isintended that the present subject matter covers all such modificationsand variations within the scope of the appended claims and theirequivalents. These and other modifications and variations to the presentinvention may be practiced by those of ordinary skill in the art,without departing from the scope of the present invention, which is moreparticularly set forth in the appended claims. Furthermore, those ofordinary skill in the art will appreciate that the foregoing descriptionis by way of example only, and is not intended to limit the invention.

What is claimed is:
 1. An optoelectronic device comprising: a substrateformed of magnesium oxide; and a multi-region stack epitaxiallydeposited upon the substrate, wherein the multi-region stack comprises anon-polar crystalline material structure along a growth direction,wherein the multi-region stack comprises: a first region comprising acrystal structure improvement layer; a second region on the first regionand comprising a first conductivity type; a third region comprising anintrinsic conductivity type layer; and a fourth region comprising asecond conductivity type, the second conductivity type being oppositethe first conductivity type, wherein the third region is between thesecond region and the fourth region; wherein at least one region of themulti-region stack is a bulk semiconductor material comprisingMg_((x))Zn_((1-x))O; wherein at least one region of the multi-regionstack is a superlattice comprising MgO and Mg_((x))Zn_((1-x))O; andwherein the Mg_((x))Zn_((1-x))O of the bulk semiconductor material orthe superlattice is a non-polar rocksalt, and x>0.55.
 2. Theoptoelectronic device of claim 1, wherein at least one of the secondregion or the fourth region is formed by introducing at least one ofsilicon, germanium, nitrogen, aluminum, gallium, nickel or phosphorousinto the non-polar crystalline material structure.
 3. The optoelectronicdevice of claim 1, wherein: at least one of the second region or thefourth region comprises a second superlattice, the second superlatticehaving a plurality of bilayer pairs formed of Mg_((x))M_((1-x))O andMg_((y))M_((1-y))O, wherein x≠y and M is selected from Zn, Al, Ga, Ni,N, and P; the second superlattice is formed using compositional gradingof an effective alloy composition of the second superlattice; and theeffective alloy composition of the second superlattice varies along thegrowth direction.
 4. The optoelectronic device of claim 1, wherein themulti-region stack consists of Mg_((x))M_((1-x))O compositions, where0.55<x≤1.0, and M is selected from Zn, Al, Ga, Ni, N, and P.
 5. Theoptoelectronic device of claim 1, further comprising a buffer layerbetween the substrate and the first region.
 6. The optoelectronic deviceof claim 5, wherein the buffer layer is made of MgZnO.
 7. Theoptoelectronic device of claim 1, wherein the first region comprises thesuperlattice formed of a plurality of alternating sub-layers of the MgOand the Mg_((x))Zn_((1-x))O.
 8. An optoelectronic device comprising: asubstrate formed of magnesium oxide; and a multi-region stackepitaxially deposited upon the substrate, wherein the multi-region stackcomprises a crystal polarity having an oxygen-polar crystal structure ora metal-polar crystal structure along a growth direction, and whereinthe multi-region stack comprises: a first region comprising a crystalstructure improvement layer; a second region on the first region andcomprising a first conductivity type; a third region comprising anintrinsic conductivity type layer; and a fourth region comprising asecond conductivity type, the second conductivity type being oppositethe first conductivity type, wherein the third region is between thesecond region and the fourth region; wherein at least one region of themulti-region stack is a bulk semiconductor material comprisingMg_((x))Zn_((1-x))O; wherein at least one region of the multi-regionstack is a superlattice comprising MgO and Mg_((x))Zn_((1-x))O; andwherein the Mg_((x))Zn_((1-x))O of the bulk semiconductor material orthe superlattice has x<0.45.
 9. The optoelectronic device of claim 8,wherein at least one of the second region or the fourth region is formedby introducing at least one of silicon, germanium, nitrogen, aluminum,gallium, nickel, or phosphorous into the oxygen-polar crystal structureor the metal-polar crystal structure.
 10. The optoelectronic device ofclaim 8, wherein at least one of the second region or the fourth regionis formed using compositional grading of the Mg_((x))Zn_((1-x))O of thebulk semiconductor material in which x is spatially dependent and variesalong the growth direction.
 11. The optoelectronic device of claim 8,wherein: at least one of the second region or the fourth regioncomprises the superlattice, the superlattice having a plurality ofbilayer pairs formed of Mg_((x))Zn_((1-x))O and Mg_((y))Zn_((1-y))O,wherein x≠y; the superlattice is formed using compositional grading ofan effective alloy composition of the superlattice; and the effectivealloy composition of the superlattice varies spatially along the growthdirection.
 12. The optoelectronic device of claim 11, wherein thecompositional grading comprises alternating sub-layers ofMg_((x))Zn_((1-x))O and Mg_((y))Zn_((1-y))O, where x and y change alongthe growth direction.
 13. The optoelectronic device of claim 8, furthercomprising a buffer layer between the substrate and the first region.14. The optoelectronic device of claim 13, wherein the buffer layer ismade of MgZnO.
 15. The optoelectronic device of claim 8, wherein thefirst region comprises the superlattice formed of a plurality ofalternating sub-layers of the MgO and the Mg_((x))Zn_((1-x))O.